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Anatomical aspects of the gynoecium of species of Anthurium sect. Urospadix Engl. (Araceae, Alismatales)
Flora 207 (2012) 615–621
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Anatomical aspects of the gynoecium of species of Anthurium sect. Urospadix Engl. (Araceae, Alismatales) Letícia Peres Poli a,∗ , Lívia Godinho Temponi b , Alessandra Ike Coan a a b
Departamento de Botânica, Instituto de Biociências de Rio Claro, Universidade Estadual Paulista – UNESP, C.P. 199, 13506-900 – Rio Claro, SP, Brazil Centro de Ciências Biológicas e da Saúde, Universidade Estadual do Oeste do Paraná, C.P. 701, 85819-110 – Cascavel, PR, Brazil
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Article history: Received 10 November 2011 Accepted 11 May 2012 Keywords: Floral anatomy Mucilage Secretory trichomes Stigma Stylar canal Transmitting tissue
a b s t r a c t Anthurium sect. Urospadix includes approximately 70 species differently distributed in Eastern Brazil, Western South America, and Central America. The present work studied the gynoecia of species of section Urospadix to describe their anatomical features. In all the species studied, the apical portion of the gynoecium differentiates into a stigma covered with short trichomes and an adjacent region formed by isodiametric cells. The stylar canal comprises short, unicellular secretory trichomes extending up to the ovarian aperture. Carpels are apically symplicate and basally synascidiate with a septum that does not reach the apical portion of the locule. The apical portion of the septum differentiates into long, secretory trichomes while the subapical one differentiates into the placenta. Locules are filled with mucilage. Since the epidermis of the region adjacent to the stigma, the length of the stylar portion, and the number of cell layers of the ovarian septum vary among the species studied, they may be useful for further taxonomic and systematic purposes. The present work is the first detailed report of trichome location and distribution on the gynoecia of Anthurium. © 2012 Elsevier GmbH. All rights reserved.
Introduction The family Araceae comprises 113 genera and 3174 species (The Plant List, 2010), mainly distributed in the tropics (Govaerts et al., 2002; Stevens, 2011). This family can be characterized by its inflorescence comprising a bract named spathe and a spadix containing small, actinomorphic flowers, and by its syncarpous gynoecium (Grayum, 1990). According to the current classification based on molecular phylogenetic analyses, the Araceae family is divided in 8 subfamilies (Cabrera et al., 2008): Aroideae Juss., Gymnostachydoideae Bogner & Nicolson, Lasioideae Engl., Lemnoideae Engl., Monsteroideae Schott, Orontioideae Mayo, Bogner & Boyce, Pothoideae Engl., and Zamioculcadoideae Bogner & Hesse. The subfamily Pothoideae comprises circa 920 species divided into two tribes: Potheae, which includes Pedicellarum M. Hotta, Pothoidium Schott and Pothos L., and the monogeneric Anthurieae (Cabrera et al., 2008; The Plant List, 2010). Anthurium Schott is the largest genus of the family, with approximately 862 neotropical species (The Plant List, 2010), distributed from Mexico to Argentina, as well as in the Caribbean (Mayo et al.,
∗ Corresponding author. Tel.: +55 19 3526 4215. E-mail addresses: [email protected] (L.P. Poli), [email protected] (L.G. Temponi), [email protected] (A.I. Coan). 0367-2530/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.flora.2012.06.014
1997; Govaerts et al., 2002). In Brazil, it is represented by circa 120 species spread in most phytogeographic regions: Amazonian forest, Caatinga, Cerrado, Atlantic forest and Pantanal (Coelho and Temponi, 2012). The inflorescence usually presents a persistent spathe and a spadix composed of bisexual flowers with four tepals, four free stamens, and a bilocular ovary in which one to three ovules are arranged in axile-apical or axile placentation (Mayo et al., 1997; Temponi, 2006). Since the systematics of Anthurium, which comprises 16–19 sections (Croat and Sheffer, 1983; Engler, 1878, 1898, 1905), was delimited according to a few morphological features, it is controversial and weakly supported. Anthurium sect. Urospadix includes circa 70 species differently distributed in Eastern Brazil, Western South America, and Central America (Coelho et al., 2009; Croat and Sheffer, 1983; Govaerts et al., 2002; Temponi, 2006). It is divided into seven subsections only defined according to leaf features (Engler, 1905), although the Araceae family presents heterophylly and a high phenotypic plasticity (Temponi et al., 2005). Anatomical data of reproductive organs help to better understand the taxonomy and phylogeny of Araceae. Among them, reports of structural differences of the reproductive parts between Araceae and Acorus L. have suggested to place the latter in a separate family, the Acoraceae (e.g. Eyde et al., 1967; Grayum, 1991; Rudall and Furness, 1997). Relevance of endothecial thickening patterns for infrafamiliar classification has been emphasized (French, 1985a,b, 1986). In Philodendron Schott (Mayo, 1989), gynoecial features were shown to be important at subgeneric
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Table 1 Species studied of Anthurium with respective collector numbers and herbaria. Sections/species Anthurium sect. Cardiolonchium Schott Anthurium crystallinum Linden & André Anthurium sect. Dactyophyllium Schott Anthurium pentaphyllum (Aubl.) G. Don Anthurium sect. Urospadix Engl. Anthurium acutum N.E. Br Anthurium comtum Schott Anthurium coriaceum G. Don Anthurium gladiifolium Schott Anthurium loefgrenii Engl. Anthurium longipes N.E. Br Anthurium minarum Sakuragui & Mayo Anthurium organense Engl. Anthurium parasiticum (Vell.) Stellfeld
Collector numbers (Herbaria) Temponi 300 (SPF) Temponi 119 (VIC), Temponi 344 (SPF) Gonc¸alves 320 (UB) Nadruz 1402 (RB), Temponi 313 (SPF) Temponi 297 (SPF), Temponi & Abreu 326 (SPF) Temponi 272 (SPF) Temponi 743 (UNOP) Temponi 339 (SPF) Temponi 366 (SPF) Temponi 347 (SPF) Temponi 413 (SPF)
and sectional levels. In a wider context, detailed analyses of gynoecia and ovules of basal monocotyledons (Igersheim et al., 2000) and comparisons of the floral development of Araceae and Acoraceae (Buzgo, 2001) contributed to better understand gynoecial evolution within angiosperms. Nevertheless, studies of floral anatomy in Anthurium are still scarce, but necessary. In a systematic treatment of Anthurium sect. Urospadix, Temponi (2006) pointed out the need for detailed research on gynoecia to confirm the occurrence of ovarian trichomes and variations in placentation as potential taxonomic characters. More recently, Barabé and Lacroix (2008), who studied inflorescence development in Anthurium jenmanii Engl. (Anthurium sect. Pachyneurium Schott), stressed the importance of anatomical studies of a higher number of species in order to support the systematics of Araceae. To bring forth more anatomical features on the flowers of Anthurium, the present study describes the gynoecia of 11 species of section Urospadix and relatives.
Materials and methods Samples of 11 species of Anthurium (Table 1) were collected in the Atlantic forest, on the eastern coast of Brazil, and deposited at the herbaria UB, RB, SPF, VIC – acronyms according Index Herbariorum (Holmgren et al., 1990), and at the herbarium of the Universidade Estadual do Oeste do Paraná (UNOP). Out of these 11 species, nine belong to section Urospadix, one to section Cardiolonchium Schott and one to section Dactyophyllium Schott. Inflorescences of all species were collected at various developmental stages. They were fixed in Transeau solution (Bicudo and Menezes, 2006) or FAA 50 (Johansen, 1940) and then transferred into 70% ethanol with few drops of glycerin. The fixed samples were dehydrated through a normal butyl alcohol series (Feder and O’Brien, 1968) or a butyl series with chloroform (Purvis et al., 1964) and embedded in 2-hydroxyethyl methacrylate (Historesin, Leica, D). The material was sectioned at 7 m using a rotary microtome and sections were stained with toluidine blue and basic fuchsin (Kraus and Arduin, 1997), periodic acid–Schiff (PAS reaction) and toluidine blue (Feder and O’Brien, 1968), or toluidine blue alone (Feder and O’Brien, 1968), and then mounted in EntellanTM (Merck, D). Photomicrographs were taken with a Leica DFC-290 digital camera coupled to a Leica DMLB microscope, using the Leica LAS (Leica Application Suite v. 3.3.0) image capture software.
Results In all Anthurium species studied the apical portion of the gynoecium is composed of a central region, the stigma, and an adjacent one (Figs. 1 and 2). The slit-like stigma (Fig. 2) is covered with an epidermis differentiated into short, unicellular secretory trichomes extending up to the stylar canal (Figs. 3–5). The epidermis of the region contiguous to the stigma is formed by one layer of isodiametric cells covered with a thin cuticle (Figs. 1 and 3). Anthurium pentaphyllum (A. sect. Dactyophyllium) was the only one to present papillate epidermal cells in this region (Fig. 4). The epidermal cells of A. crystallinum (A. sect. Cardiolonchium) showed accumulation of phenolic substances (Fig. 5). The style (Figs. 6–8) varies in length according to species. It is ca. one third of the gynoecium length in A. acutum, A. comtum, A. crystallinum, A. gladiifolium (Fig. 6), A. loefgrenii, A. minarum, A. organense and A. parasiticum, and half of it in A. longipes (Fig. 7), A. coriaceum (Fig. 8) and A. pentaphyllum. It is covered with an outer epidermis formed by one layer of isodiametric cells with a thin cuticle (Fig. 9). The mesophyll is parenchymatous with a variable quantity of phenolic and crystalliferous idioblasts (Figs. 4–10), the latter containing druses or raphides (Figs. 4 and 6–10). In immature gynoecia, the epidermis of the stylar canal is formed by one layer of isodiametric cells (Figs. 6, 8 and 10). As they mature, these cells differentiate into short, unicellular secretory trichomes to constitute the transmitting tissue (Figs. 3–5 and 7). Close to the apical portion of the ovary (aperture), the trichomes of this transmitting tissue become elongate (Figs. 7 and 10). In an advanced, post-fertilization stage, stylar canal is closed by the intertwining of secretory trichomes, which accumulate phenolic substances (Figs. 11–13). The gynoecium is bicarpellate and bilocular (Figs. 6–8 and 14). The carpels are apically symplicate and basally synascidiate (Figs. 6–8 and 14). The ovarian locules are separated by a thin septum in all the species studied (Figs. 6 and 8) except in A. longipes where these structures comprise more than ten cell layers (Figs. 7 and 14). Median longitudinal sections show that the septum does not reach the apical portion of the locule, where the stylar canal opens (Figs. 7, 10, 12, 14 and 15). The locules are filled with mucilage (Figs. 6, 10, 12 and 15–19). The apical portion of the septum differentiates into long, secretory unicellular trichomes (Figs. 10, 15 and 19) while the subapical portion differentiates into the placenta (Figs. 1, 6, 7 and 14). Placentation is axile in all the species studied (Figs. 1, 6, 7 and 14). Each locule presents a pendulous, bitegmic and anatropous ovule (Fig. 14). In all the species studied, ovules do not fill the locule completely (Figs. 1 and 6), except in A. longipes whose ovules contact the ovary wall (Figs. 7 and 14). The ovary wall is formed by the outer and inner epidermis, both being uniseriate, and by a parenchymatous mesophyll, with a variable quantity of idioblasts containing druses and raphides (Figs. 18 and 19).
Discussion Although due to the limited number of investigated species generalizations concerning gynoecial structure and evolution in Araceae might be premature, the present data highlight relevant anatomical aspects to characterize the mature gynoecium of species of Anthurium sect. Urospadix. All the species studied present: (i) an apical portion of the gynoecium differentiated into a stigma covered with short trichomes and an adjacent region formed by isodiametric cells; (ii) an anatomically differentiated style with a mesophyll rich in phenolic or crystalliferous idioblasts; (iii) a stylar canal which is formed by short, unicellular secretory trichomes that extend to the ovarian aperture; (iv) carpels which are apically
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Figs. 1–5. Anatomical aspects of gynoecia of species of Anthurium sect. Urospadix (1–3), A. sect. Dactyophyllium (4) and A. sect. Cardiolonchium (5). 1. Longitudinal section (LS) of mature gynoecium of A. gladiifolium showing stigma, style and ovarian locules. 2. Transversal section (TS) of immature gynoecial apex of A. comtum showing the stigmatic region. 3. Median LS of a developing gynoecium of A. comtum showing stigma and transmitting tissue formed by unicellular trichomes. 4. LS of a mature gynoecium of A. pentaphyllum showing the adjacent region covered by a papillate epidermis. 5. Detail of the mature gynoecial apex in A. crystallinum, showing epidermal cells of the region adjacent to the stigma filled with phenolic substances, in LS. e, epidermis; ov, ovule; st, stigma; tr, trichomes. Scale bars: 1, 3–5 = 100 m; 2 = 150 m.
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Figs. 6–10. Anatomical aspects of immature (7, 10) and mature (6, 8, 9) gynoecia of species of Anthurium sect. Urospadix. 6–8. Longitudinal sections (LS) of A. gladiifolium (6), A. longipes (7) and A. coriaceum (8), showing apically symplicate and basally synascidiate carpels and variation in length of styles and in width of ovarian septa. 9. Transversal section (TS) of the style of A. organense showing phenolic idioblasts and transmitting tissue. 10. LS of the gynoecium of A. gladiifolium showing the developing stylar canal with trichomes in its proximal region and in the apex of the ovarian septum. Asterisk, mucilage; ov, ovule; sc, stylar canal; tr, trichomes. Scale bars: 8 = 100 m; 6, 9–10 = 150 m; 7 = 20 m.
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Figs. 11–14. Longitudinal sections of mature gynoecia of species of Anthurium sect. Urospadix (11–12, 14) and A. sect. Dactyophyllium (13). 11–13. Details of stigmas and stylar canals showing intertwining secretory trichomes in A. acutum (11), A. minarum (12), and A. pentaphyllum (13). 14. Detail of the ovarian region in A. longipes showing the bicarpellate and bilocular gynoecium with axial placentation. ov, ovule; sc, stylar canal; se, septum; tr, trichomes. Scale bars: 11 = 200 m; 12 = 100 m; 13–14 = 150 m.
symplicate and basally synascidiate, with a septum that does not reach the apical portion of the locule; (v) an apical portion of the septum having long, secretory trichomes and a subapical portion forming the placenta; and (vi) ovarian locules filled with mucilage. In principle, uniformity was found between the anatomical aspects of the gynoecia of the Anthurium sect. Urospadix species and those of two species which belong to other sections (A. crystallinum – sect. Cardiolonchium, and A. pentaphyllum – sect. Dactyophyllium). However, the epidermal cells in the region adjacent to the stigma have different features: in the species belonging to section Urospadix they are isodiametric, without any different content or shape, while in the two species from the other sections they showed variations, e.g. accumulation of phenolic substances in A. crystallinum (A. sect. Cardiolonchium) and papillate shape in A.
pentaphyllum (A. sect. Dactyophyllium). The occurrence of papillate cells in gynoecia has already been mentioned for Pothos latifolius L. (Eyde et al., 1967), and phenolic substances were considered a valuable taxonomic feature for the infrageneric characterization of Philodendron (Mayo, 1989). Evidence shows that these characters together with external morphological data may be useful for the systematics of Araceae at the generic level. The stigma of Araceae is usually described as sessile or almost sessile (Croat, 1980; Mayo et al., 1997). Nonetheless, the species of Anthurium studied here present a region between stigma and ovary, which is anatomically distinct and varies in length. In the species studied, the epidermis of stigma and stylar canal is formed by unicellular trichomes. This is the case of most genera in Araceae, including Pothos L. and Pothoidium Schott (Buzgo,
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Figs. 15–19. Anatomical aspects of mature gynoecia of species of Anthurium sect. Dactyophyllium (15, 17–19) and A. sect. Urospadix (16). 15. Detail of a mature ovarian aperture and incomplete septum of A. pentaphyllum, covered with long secretory trichomes, in longitudinal section (LS). 16. Transversal section (TS) of the ovary of A. comtum, in the region of ovarian aperture. 17–19. Successive TS of the mature ovary of A. pentaphyllum showing the symplicate region (17), the beginning of the synascidiate region (18), and the synascidiate region (19). Asterisk, mucilage; tr, trichomes. Scale bars: 15–17 = 100 m; 16, 18–19 = 150 m.
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2001), which belong to the sister-group of Anthurium (Cabrera et al., 2008). Apparently this character is widespread among Pothoideae. However, intertwining of secretory trichomes, which accumulate phenolic substances after fertilization, has never been described in previous studies (e.g. Barabé and Lacroix, 2008; Buzgo, 2001; Eyde et al., 1967; Igersheim et al., 2000). It is reported for the first time here, although it probably occurs in Pothos, Pothoidium and other genera of Araceae with similar stigma and transmitting tissue, too. In all species studied here, the apical portion of the septum differentiates into unicellular, long trichomes, which secret mucilage that completely fills the locules. Secretory trichomes in ovary is a widely distributed character among monocotyledons (Rudall et al., 1998) and it is present in most genera of Araceae, except Gymnostachys R. Br., Simplocarpus F. Schmidt, and some species of Theriophonum Blume, Typhonium Schott, Arisaema Mart (French, 1987) and Pothos (Eyde et al., 1967; Igersheim et al., 2000). Despite the proximity between Anthurium and Pothos, this character presented no variations in the species studied of section Urospadix and in those of sections Cardiolonchium and Dactyophyllium. Such results suggest that it may be uniform in Anthurium and may help segregate species or bigger groups within other genera of Araceae. Although French (1987) had already mentioned these trichomes in Anthurium, their location and distribution on the gynoecium are reported for the first time in the present study. The carpels of all the species studied here are apically symplicate and basally synascidiate. This had already been reported for Pothos and other genera of the family such as Spathiphyllum Schott (Buzgo, 2001). As it is evidenced for Anthurium here, the septa do not reach the apex of the ovary, the transmitting tissue continues up to septum center, and the placentation is axial. This all is in accordance with the results described by Buzgo (2001) for the sister-group Potheae, underling the relationships. An axile placentation was previously observed also in Philodendron by Mayo (1989). According to this author, in Philodendron, the entry of the stylar canal into the ovary is correlated with the type of placentation. Hence, he considered placentation as axial when the stylar canal enters into the apical, subapical or median region of the ovary. In the species of Anthurium studied here, the stylar canal enters the apical portion of the ovary and the ovules are inserted in the subapical portion of the septum. This conforms the previously described axial placentation in Philodendron and documented now also in Anthurium. The anatomical aspects of mature gynoecia of species of Anthurium have great similarity with Pothos, reaffirming the sister-group relationship and the insertion of Anthurium into the subfamily Pothoideae. The present study also confirms the continuous occurrence of trichomes from the stigma to the septum apex, describing their distribution on the gynoecia of several Anthurium species. Moreover, the results also contribute further knowledge about the axial placentation in the genus – which previously was observed only from herbarium material and/or under stereomicroscope analysis. Acknowledgements Financial support was provided by Fundac¸ão Araucária (edital no. 003/2009-PRPPG; proc. 223/2010), Fundac¸ão de Amparo à Pesquisa do Estado de São Paulo – FAPESP (proc. 2011/03358-8; proc. 2010/17400-3), and Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (proc. 475212/2011-8).
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Flora journal homepage: www.elsevier.de/flora
Anatomical aspects of the gynoecium of species of Anthurium sect. Urospadix Engl. (Araceae, Alismatales) Letícia Peres Poli a,∗ , Lívia Godinho Temponi b , Alessandra Ike Coan a a b
Departamento de Botânica, Instituto de Biociências de Rio Claro, Universidade Estadual Paulista – UNESP, C.P. 199, 13506-900 – Rio Claro, SP, Brazil Centro de Ciências Biológicas e da Saúde, Universidade Estadual do Oeste do Paraná, C.P. 701, 85819-110 – Cascavel, PR, Brazil
a r t i c l e
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Article history: Received 10 November 2011 Accepted 11 May 2012 Keywords: Floral anatomy Mucilage Secretory trichomes Stigma Stylar canal Transmitting tissue
a b s t r a c t Anthurium sect. Urospadix includes approximately 70 species differently distributed in Eastern Brazil, Western South America, and Central America. The present work studied the gynoecia of species of section Urospadix to describe their anatomical features. In all the species studied, the apical portion of the gynoecium differentiates into a stigma covered with short trichomes and an adjacent region formed by isodiametric cells. The stylar canal comprises short, unicellular secretory trichomes extending up to the ovarian aperture. Carpels are apically symplicate and basally synascidiate with a septum that does not reach the apical portion of the locule. The apical portion of the septum differentiates into long, secretory trichomes while the subapical one differentiates into the placenta. Locules are filled with mucilage. Since the epidermis of the region adjacent to the stigma, the length of the stylar portion, and the number of cell layers of the ovarian septum vary among the species studied, they may be useful for further taxonomic and systematic purposes. The present work is the first detailed report of trichome location and distribution on the gynoecia of Anthurium. © 2012 Elsevier GmbH. All rights reserved.
Introduction The family Araceae comprises 113 genera and 3174 species (The Plant List, 2010), mainly distributed in the tropics (Govaerts et al., 2002; Stevens, 2011). This family can be characterized by its inflorescence comprising a bract named spathe and a spadix containing small, actinomorphic flowers, and by its syncarpous gynoecium (Grayum, 1990). According to the current classification based on molecular phylogenetic analyses, the Araceae family is divided in 8 subfamilies (Cabrera et al., 2008): Aroideae Juss., Gymnostachydoideae Bogner & Nicolson, Lasioideae Engl., Lemnoideae Engl., Monsteroideae Schott, Orontioideae Mayo, Bogner & Boyce, Pothoideae Engl., and Zamioculcadoideae Bogner & Hesse. The subfamily Pothoideae comprises circa 920 species divided into two tribes: Potheae, which includes Pedicellarum M. Hotta, Pothoidium Schott and Pothos L., and the monogeneric Anthurieae (Cabrera et al., 2008; The Plant List, 2010). Anthurium Schott is the largest genus of the family, with approximately 862 neotropical species (The Plant List, 2010), distributed from Mexico to Argentina, as well as in the Caribbean (Mayo et al.,
∗ Corresponding author. Tel.: +55 19 3526 4215. E-mail addresses: [email protected] (L.P. Poli), [email protected] (L.G. Temponi), [email protected] (A.I. Coan). 0367-2530/$ – see front matter © 2012 Elsevier GmbH. All rights reserved. http://dx.doi.org/10.1016/j.flora.2012.06.014
1997; Govaerts et al., 2002). In Brazil, it is represented by circa 120 species spread in most phytogeographic regions: Amazonian forest, Caatinga, Cerrado, Atlantic forest and Pantanal (Coelho and Temponi, 2012). The inflorescence usually presents a persistent spathe and a spadix composed of bisexual flowers with four tepals, four free stamens, and a bilocular ovary in which one to three ovules are arranged in axile-apical or axile placentation (Mayo et al., 1997; Temponi, 2006). Since the systematics of Anthurium, which comprises 16–19 sections (Croat and Sheffer, 1983; Engler, 1878, 1898, 1905), was delimited according to a few morphological features, it is controversial and weakly supported. Anthurium sect. Urospadix includes circa 70 species differently distributed in Eastern Brazil, Western South America, and Central America (Coelho et al., 2009; Croat and Sheffer, 1983; Govaerts et al., 2002; Temponi, 2006). It is divided into seven subsections only defined according to leaf features (Engler, 1905), although the Araceae family presents heterophylly and a high phenotypic plasticity (Temponi et al., 2005). Anatomical data of reproductive organs help to better understand the taxonomy and phylogeny of Araceae. Among them, reports of structural differences of the reproductive parts between Araceae and Acorus L. have suggested to place the latter in a separate family, the Acoraceae (e.g. Eyde et al., 1967; Grayum, 1991; Rudall and Furness, 1997). Relevance of endothecial thickening patterns for infrafamiliar classification has been emphasized (French, 1985a,b, 1986). In Philodendron Schott (Mayo, 1989), gynoecial features were shown to be important at subgeneric
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Table 1 Species studied of Anthurium with respective collector numbers and herbaria. Sections/species Anthurium sect. Cardiolonchium Schott Anthurium crystallinum Linden & André Anthurium sect. Dactyophyllium Schott Anthurium pentaphyllum (Aubl.) G. Don Anthurium sect. Urospadix Engl. Anthurium acutum N.E. Br Anthurium comtum Schott Anthurium coriaceum G. Don Anthurium gladiifolium Schott Anthurium loefgrenii Engl. Anthurium longipes N.E. Br Anthurium minarum Sakuragui & Mayo Anthurium organense Engl. Anthurium parasiticum (Vell.) Stellfeld
Collector numbers (Herbaria) Temponi 300 (SPF) Temponi 119 (VIC), Temponi 344 (SPF) Gonc¸alves 320 (UB) Nadruz 1402 (RB), Temponi 313 (SPF) Temponi 297 (SPF), Temponi & Abreu 326 (SPF) Temponi 272 (SPF) Temponi 743 (UNOP) Temponi 339 (SPF) Temponi 366 (SPF) Temponi 347 (SPF) Temponi 413 (SPF)
and sectional levels. In a wider context, detailed analyses of gynoecia and ovules of basal monocotyledons (Igersheim et al., 2000) and comparisons of the floral development of Araceae and Acoraceae (Buzgo, 2001) contributed to better understand gynoecial evolution within angiosperms. Nevertheless, studies of floral anatomy in Anthurium are still scarce, but necessary. In a systematic treatment of Anthurium sect. Urospadix, Temponi (2006) pointed out the need for detailed research on gynoecia to confirm the occurrence of ovarian trichomes and variations in placentation as potential taxonomic characters. More recently, Barabé and Lacroix (2008), who studied inflorescence development in Anthurium jenmanii Engl. (Anthurium sect. Pachyneurium Schott), stressed the importance of anatomical studies of a higher number of species in order to support the systematics of Araceae. To bring forth more anatomical features on the flowers of Anthurium, the present study describes the gynoecia of 11 species of section Urospadix and relatives.
Materials and methods Samples of 11 species of Anthurium (Table 1) were collected in the Atlantic forest, on the eastern coast of Brazil, and deposited at the herbaria UB, RB, SPF, VIC – acronyms according Index Herbariorum (Holmgren et al., 1990), and at the herbarium of the Universidade Estadual do Oeste do Paraná (UNOP). Out of these 11 species, nine belong to section Urospadix, one to section Cardiolonchium Schott and one to section Dactyophyllium Schott. Inflorescences of all species were collected at various developmental stages. They were fixed in Transeau solution (Bicudo and Menezes, 2006) or FAA 50 (Johansen, 1940) and then transferred into 70% ethanol with few drops of glycerin. The fixed samples were dehydrated through a normal butyl alcohol series (Feder and O’Brien, 1968) or a butyl series with chloroform (Purvis et al., 1964) and embedded in 2-hydroxyethyl methacrylate (Historesin, Leica, D). The material was sectioned at 7 m using a rotary microtome and sections were stained with toluidine blue and basic fuchsin (Kraus and Arduin, 1997), periodic acid–Schiff (PAS reaction) and toluidine blue (Feder and O’Brien, 1968), or toluidine blue alone (Feder and O’Brien, 1968), and then mounted in EntellanTM (Merck, D). Photomicrographs were taken with a Leica DFC-290 digital camera coupled to a Leica DMLB microscope, using the Leica LAS (Leica Application Suite v. 3.3.0) image capture software.
Results In all Anthurium species studied the apical portion of the gynoecium is composed of a central region, the stigma, and an adjacent one (Figs. 1 and 2). The slit-like stigma (Fig. 2) is covered with an epidermis differentiated into short, unicellular secretory trichomes extending up to the stylar canal (Figs. 3–5). The epidermis of the region contiguous to the stigma is formed by one layer of isodiametric cells covered with a thin cuticle (Figs. 1 and 3). Anthurium pentaphyllum (A. sect. Dactyophyllium) was the only one to present papillate epidermal cells in this region (Fig. 4). The epidermal cells of A. crystallinum (A. sect. Cardiolonchium) showed accumulation of phenolic substances (Fig. 5). The style (Figs. 6–8) varies in length according to species. It is ca. one third of the gynoecium length in A. acutum, A. comtum, A. crystallinum, A. gladiifolium (Fig. 6), A. loefgrenii, A. minarum, A. organense and A. parasiticum, and half of it in A. longipes (Fig. 7), A. coriaceum (Fig. 8) and A. pentaphyllum. It is covered with an outer epidermis formed by one layer of isodiametric cells with a thin cuticle (Fig. 9). The mesophyll is parenchymatous with a variable quantity of phenolic and crystalliferous idioblasts (Figs. 4–10), the latter containing druses or raphides (Figs. 4 and 6–10). In immature gynoecia, the epidermis of the stylar canal is formed by one layer of isodiametric cells (Figs. 6, 8 and 10). As they mature, these cells differentiate into short, unicellular secretory trichomes to constitute the transmitting tissue (Figs. 3–5 and 7). Close to the apical portion of the ovary (aperture), the trichomes of this transmitting tissue become elongate (Figs. 7 and 10). In an advanced, post-fertilization stage, stylar canal is closed by the intertwining of secretory trichomes, which accumulate phenolic substances (Figs. 11–13). The gynoecium is bicarpellate and bilocular (Figs. 6–8 and 14). The carpels are apically symplicate and basally synascidiate (Figs. 6–8 and 14). The ovarian locules are separated by a thin septum in all the species studied (Figs. 6 and 8) except in A. longipes where these structures comprise more than ten cell layers (Figs. 7 and 14). Median longitudinal sections show that the septum does not reach the apical portion of the locule, where the stylar canal opens (Figs. 7, 10, 12, 14 and 15). The locules are filled with mucilage (Figs. 6, 10, 12 and 15–19). The apical portion of the septum differentiates into long, secretory unicellular trichomes (Figs. 10, 15 and 19) while the subapical portion differentiates into the placenta (Figs. 1, 6, 7 and 14). Placentation is axile in all the species studied (Figs. 1, 6, 7 and 14). Each locule presents a pendulous, bitegmic and anatropous ovule (Fig. 14). In all the species studied, ovules do not fill the locule completely (Figs. 1 and 6), except in A. longipes whose ovules contact the ovary wall (Figs. 7 and 14). The ovary wall is formed by the outer and inner epidermis, both being uniseriate, and by a parenchymatous mesophyll, with a variable quantity of idioblasts containing druses and raphides (Figs. 18 and 19).
Discussion Although due to the limited number of investigated species generalizations concerning gynoecial structure and evolution in Araceae might be premature, the present data highlight relevant anatomical aspects to characterize the mature gynoecium of species of Anthurium sect. Urospadix. All the species studied present: (i) an apical portion of the gynoecium differentiated into a stigma covered with short trichomes and an adjacent region formed by isodiametric cells; (ii) an anatomically differentiated style with a mesophyll rich in phenolic or crystalliferous idioblasts; (iii) a stylar canal which is formed by short, unicellular secretory trichomes that extend to the ovarian aperture; (iv) carpels which are apically
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Figs. 1–5. Anatomical aspects of gynoecia of species of Anthurium sect. Urospadix (1–3), A. sect. Dactyophyllium (4) and A. sect. Cardiolonchium (5). 1. Longitudinal section (LS) of mature gynoecium of A. gladiifolium showing stigma, style and ovarian locules. 2. Transversal section (TS) of immature gynoecial apex of A. comtum showing the stigmatic region. 3. Median LS of a developing gynoecium of A. comtum showing stigma and transmitting tissue formed by unicellular trichomes. 4. LS of a mature gynoecium of A. pentaphyllum showing the adjacent region covered by a papillate epidermis. 5. Detail of the mature gynoecial apex in A. crystallinum, showing epidermal cells of the region adjacent to the stigma filled with phenolic substances, in LS. e, epidermis; ov, ovule; st, stigma; tr, trichomes. Scale bars: 1, 3–5 = 100 m; 2 = 150 m.
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Figs. 6–10. Anatomical aspects of immature (7, 10) and mature (6, 8, 9) gynoecia of species of Anthurium sect. Urospadix. 6–8. Longitudinal sections (LS) of A. gladiifolium (6), A. longipes (7) and A. coriaceum (8), showing apically symplicate and basally synascidiate carpels and variation in length of styles and in width of ovarian septa. 9. Transversal section (TS) of the style of A. organense showing phenolic idioblasts and transmitting tissue. 10. LS of the gynoecium of A. gladiifolium showing the developing stylar canal with trichomes in its proximal region and in the apex of the ovarian septum. Asterisk, mucilage; ov, ovule; sc, stylar canal; tr, trichomes. Scale bars: 8 = 100 m; 6, 9–10 = 150 m; 7 = 20 m.
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Figs. 11–14. Longitudinal sections of mature gynoecia of species of Anthurium sect. Urospadix (11–12, 14) and A. sect. Dactyophyllium (13). 11–13. Details of stigmas and stylar canals showing intertwining secretory trichomes in A. acutum (11), A. minarum (12), and A. pentaphyllum (13). 14. Detail of the ovarian region in A. longipes showing the bicarpellate and bilocular gynoecium with axial placentation. ov, ovule; sc, stylar canal; se, septum; tr, trichomes. Scale bars: 11 = 200 m; 12 = 100 m; 13–14 = 150 m.
symplicate and basally synascidiate, with a septum that does not reach the apical portion of the locule; (v) an apical portion of the septum having long, secretory trichomes and a subapical portion forming the placenta; and (vi) ovarian locules filled with mucilage. In principle, uniformity was found between the anatomical aspects of the gynoecia of the Anthurium sect. Urospadix species and those of two species which belong to other sections (A. crystallinum – sect. Cardiolonchium, and A. pentaphyllum – sect. Dactyophyllium). However, the epidermal cells in the region adjacent to the stigma have different features: in the species belonging to section Urospadix they are isodiametric, without any different content or shape, while in the two species from the other sections they showed variations, e.g. accumulation of phenolic substances in A. crystallinum (A. sect. Cardiolonchium) and papillate shape in A.
pentaphyllum (A. sect. Dactyophyllium). The occurrence of papillate cells in gynoecia has already been mentioned for Pothos latifolius L. (Eyde et al., 1967), and phenolic substances were considered a valuable taxonomic feature for the infrageneric characterization of Philodendron (Mayo, 1989). Evidence shows that these characters together with external morphological data may be useful for the systematics of Araceae at the generic level. The stigma of Araceae is usually described as sessile or almost sessile (Croat, 1980; Mayo et al., 1997). Nonetheless, the species of Anthurium studied here present a region between stigma and ovary, which is anatomically distinct and varies in length. In the species studied, the epidermis of stigma and stylar canal is formed by unicellular trichomes. This is the case of most genera in Araceae, including Pothos L. and Pothoidium Schott (Buzgo,
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Figs. 15–19. Anatomical aspects of mature gynoecia of species of Anthurium sect. Dactyophyllium (15, 17–19) and A. sect. Urospadix (16). 15. Detail of a mature ovarian aperture and incomplete septum of A. pentaphyllum, covered with long secretory trichomes, in longitudinal section (LS). 16. Transversal section (TS) of the ovary of A. comtum, in the region of ovarian aperture. 17–19. Successive TS of the mature ovary of A. pentaphyllum showing the symplicate region (17), the beginning of the synascidiate region (18), and the synascidiate region (19). Asterisk, mucilage; tr, trichomes. Scale bars: 15–17 = 100 m; 16, 18–19 = 150 m.
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2001), which belong to the sister-group of Anthurium (Cabrera et al., 2008). Apparently this character is widespread among Pothoideae. However, intertwining of secretory trichomes, which accumulate phenolic substances after fertilization, has never been described in previous studies (e.g. Barabé and Lacroix, 2008; Buzgo, 2001; Eyde et al., 1967; Igersheim et al., 2000). It is reported for the first time here, although it probably occurs in Pothos, Pothoidium and other genera of Araceae with similar stigma and transmitting tissue, too. In all species studied here, the apical portion of the septum differentiates into unicellular, long trichomes, which secret mucilage that completely fills the locules. Secretory trichomes in ovary is a widely distributed character among monocotyledons (Rudall et al., 1998) and it is present in most genera of Araceae, except Gymnostachys R. Br., Simplocarpus F. Schmidt, and some species of Theriophonum Blume, Typhonium Schott, Arisaema Mart (French, 1987) and Pothos (Eyde et al., 1967; Igersheim et al., 2000). Despite the proximity between Anthurium and Pothos, this character presented no variations in the species studied of section Urospadix and in those of sections Cardiolonchium and Dactyophyllium. Such results suggest that it may be uniform in Anthurium and may help segregate species or bigger groups within other genera of Araceae. Although French (1987) had already mentioned these trichomes in Anthurium, their location and distribution on the gynoecium are reported for the first time in the present study. The carpels of all the species studied here are apically symplicate and basally synascidiate. This had already been reported for Pothos and other genera of the family such as Spathiphyllum Schott (Buzgo, 2001). As it is evidenced for Anthurium here, the septa do not reach the apex of the ovary, the transmitting tissue continues up to septum center, and the placentation is axial. This all is in accordance with the results described by Buzgo (2001) for the sister-group Potheae, underling the relationships. An axile placentation was previously observed also in Philodendron by Mayo (1989). According to this author, in Philodendron, the entry of the stylar canal into the ovary is correlated with the type of placentation. Hence, he considered placentation as axial when the stylar canal enters into the apical, subapical or median region of the ovary. In the species of Anthurium studied here, the stylar canal enters the apical portion of the ovary and the ovules are inserted in the subapical portion of the septum. This conforms the previously described axial placentation in Philodendron and documented now also in Anthurium. The anatomical aspects of mature gynoecia of species of Anthurium have great similarity with Pothos, reaffirming the sister-group relationship and the insertion of Anthurium into the subfamily Pothoideae. The present study also confirms the continuous occurrence of trichomes from the stigma to the septum apex, describing their distribution on the gynoecia of several Anthurium species. Moreover, the results also contribute further knowledge about the axial placentation in the genus – which previously was observed only from herbarium material and/or under stereomicroscope analysis. Acknowledgements Financial support was provided by Fundac¸ão Araucária (edital no. 003/2009-PRPPG; proc. 223/2010), Fundac¸ão de Amparo à Pesquisa do Estado de São Paulo – FAPESP (proc. 2011/03358-8; proc. 2010/17400-3), and Conselho Nacional de Desenvolvimento Científico e Tecnológico – CNPq (proc. 475212/2011-8).
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