Morphological and micromorphological characteristics of Desmodium fruits (Leguminosae: Papilionoideae)
Daiane M. Freitas1*, Ademir Reis2*, Roseli L. da Costa Bortoluzzi3* & Marisa Santos4*
Abstract
The genus Desmodium is represented in Santa Catarina State, Brazil, by 13 species, all with lomentaceous fruits. Shape, size and isthmus margin of loments vary, while the surface is glabrous, or covered by trichomes of different types. Morphological diversity of trichomes becomes particularly relevant to taxonomic description. The trichome types present on the surface of Desmodium fruits provide data for the identification and classification of species in the State. To assess this, three fruits of each species were collected and deposited at two herbaria, HBR and FLOR, in Santa Catarina, Brazil. Some rehydrated samples were examined using light microscopy (LM); and some sections were exposed to the following histochemical reagents: Sudan III for oils and Thionine for mucilage. The structural aspects of trichomes can be classified into uni- or multicel- lular and may still be simple, i.e., nonglandular or glandular. Using scanning electron microscopy (SEM), five types of trichomes were identified and analyzed among the Desmodium species studied: uncinate, uniseriate, globose multicellular, globose unicellular and subulate. Characteristics, such as loment margin and article form, glabrescent or pillous indument, trichome type, with or without papillous epidermal cells and epicuticular striations, showed relevant diagnostic value. An identification key was developed for Desmodium species from Santa Catarina State, Brazil, based on macro and micromorphological characters of the fruit.
Características morfológicas y micromorfológicos de frutos Desmodium (Leguminosae: Papilionoideae). El género Desmodium está representado en Santa Catarina, Brasil, por 13 especies, todas con frutos lomentaceos. Los lomentos han tenido variación en forma, tamaño y características del margen del istmo, y la superficie es glabra o cubierta por tricomas de diferentes tipos. La diversidad morfológica de los tricomas se vuelve particularmente relevante para la descripción taxonómica. Los tipos de tri- comas presentes en la superficie de los frutos Desmodium, proporcionan datos para la identificación y clasificación de las especies en el Estado de Santa Catarina, Brasil. Tres frutos de cada especie fueron recogidos y depositados en el Herbario (HBR y FLOR, Santa Catarina, Brasil). Algu- nas muestras fueron rehidratadas y examinadas usando microscopía de luz (LM), las secciones fueron expuestas a los siguientes reactivos histoquímicos: Sudan III para los aceites y Tionina para mucílago. Los aspectos estructurales de los tricomas se pueden clasificar en uni o multicelulares y pueden todavía ser simples, es decir, no glandular o glandular. Por medio del uso de la microscopía elec- trónica de barrido (SEM), cinco tipos de tricomas se han identificado y analizado entre las especies de Desmodium estudiadas: uncinado, uniseriado, globoso multicelular, globoso unicelular y subulado. Características como el margen del lomento y la forma del artículo, indumento glabrescente o piloso, tipo de tricomas con o sin células epidérmicas papilosas, y estrías epicuticulares mostraron valor de diagnóstico relevante. La clave de identificación fue desarrollada para especies de Desmodium del Estado de Santa Catarina, Brasil, basado en caracteres macro y micromorfológicos del fruto.
Palabras clave: dispersión, clave de identificación, microscopía electrónica de barrido (SEM), estructuras secretoras, taxonomía, tricomas.
The Desmodium Desv. genus (Legumino- sae, subfamily Papilionoideae; Ohashi, 2014) is included in the tribe Desmodieae and compris- es about 524-530 species, with greater diversity in Southeast Asia, Mexico and South America (Ohashi, 2014). According to Lima, Oliveira and Tozzi (2014), 33 species are distributed throughout Brazil and 16 species in Santa Catarina State. The genus is characterized by shrubby or subshrubby habit, uni- or trifoliate leaves, lomentaceous or craspedium-type fruit (whose pericarp splits into monospermous articles), and uncinate (hooked) ]]>
According to ]]>
Desmodium species can have glabrescent or densely pubescent fruit, and the trichomes can be uncinate or straight, uniseriate or multicellular, and long or short. Oliveira (1983, 1990) also cited different trichome types on the fruit surface for this genus: uncinate, straight glandular and straight nonglandular. Werker (2000) pointed out that trichomes are uni- or multicellular appendices originating from single epidermal cells present in various plant ]]>
Epidermal surface ornamentation, such as conformations of the outer cell wall, trichomes and epicuticular waxes, contribute to maintain- ing inner water balance ]]>
Several studies have demonstrated the use of scanning electron microscopy (SEM) in angiosperm ]]>
Quercus L. (Fagaceae) leaf surfaces could be used for delimiting species in that trichomes showed variation in shape, ]]>
Abrus Adans. (Papilionoideae). Ritter and Miotto (2006) used SEM to ]]>
Mikania Willd. (Asteraceae). Akcin (2008) identified different microstructural pat- terns on the surface of seeds and fruits from Cynoglossum L. (Boraginaceae) species. Kaya, Ünal, Özgökçe, Doğan, and Martin (2011) also used SEM to study fruit and seed surface characteristics to study the taxonomy of 11 genera of Brassicaceae. ]]>
The present research aimed to contribute to the identification and classification of the Desmodium genus from Santa Catarina State, Brazil, based on fruit macro- and ]]>
Materials and Methods
For this study, specimens with ]]>
Three ]]>
Desmodium adscendens (Sw.) DC (D. M. Freitas 82 [21/03/2010] FLOR/HBR, 165 [07/02/2011] FLOR/HBR, 179 [17/03/2011] HBR);
D. affine Schltdl. (R. Reitz & R. M. Klein 16752 [01/01/1964] HBR; D. M. Freitas 97 [21/03/2010] HBR, 192 [18/03/2011] FLOR/HBR); D. barbatum (L.) Benth. (D. M. Freitas 168 [16/03/2011] HBR, 186 [17/03/2011] FLOR/HBR, 203 [23/04/2011] FLOR/HBR); D. cuneatum ]]>
D. subsecundum Vogel (R. Reitz & R. M. Klein 3978 [13/04/1956] HBR; A. Reis & D. M. Freitas 2602 [13/02/2011] FLOR/ HBR, 2616 [23/02/2011] FLOR/HBR);
D. incanum DC. (D. M. Freitas 166 [07/02/2011] FLOR/HBR, 187 [18/03/2011] HBR, 204 [10/06/2011] FLOR/HBR); D. leiocarpum (Spreng.) G.Don. (A. Reis 2617 [08/03/2011] FLOR/HBR, 2620 [09/02/2011] FLOR/HBR; R. Reitz & R. M. Klein 12294 [22/02/1962] HBR); D. pachyrhizum Vogel (L. B. Smith & R. Reitz ]]>
D. subsericeum Malme (R. ]]>
D. tortuosum (Sw.) DC. (D. M. Freitas & A. Reis 145 [12/11/2010] FLOR/HBR; D. M. Freitas & A. Zanin 185 [17/03/2011] FLOR/HBR; A. Reis 2628 [13/03/2011] FLOR/HBR); D. triarticulatum Malme (D. M. ]]>
D. uncinatum (Jacq.) DC. (D. M. Freitas 195 [22/4/2011] FLOR/HBR; A. Reis 2623 [09/3/2011] FLOR/HBR; R. Reitz & R. M. Klein 14828 [13/4/1963] HBR).
Lima et al. (2014) reported the occur- rence of 16 species of Desmodium in ]]>
D. album, D. arechavaletae, D. triflorum and D. venosum, were not found in either HBR or FLOR, nor were they found in the many field collections covering almost every Brazilian state. Mean-while, in this investigation, the occurrence of D. leiocarpum was registered, but not previously reported to Santa Catarina State by Lima et al. (2014).
Images of fruits were captured with a stereoscopic microscope (Olympus SZ-40, Tokyo, Japan) with a digital ]]>
Three fruits of each species (total of 39 samples) were rehydrated in distilled water with some drops of detergent and heated to 90°C (Bersier & Bocquet, 1960). SEM analysis was carried out ]]>
Thirteen rehydrated samples were examined using light microscopy (LM). Further- more, two fruits of each species were freehand sectioned transversely and longitudinally, with a razor blade. Sections were exposed to the following histochemical ]]>
Results
Desmodium species have lomentaceous fruits (Fig. 1). While uncinate trichomes were observed, other types can occur, including uniseriate, globose and subulate. Loments of some Desmodium species were sinuous at both edges, or the upper edge was ]]>
Fig. 1). Two species, D. subsecundum and D. leiocarpum, had glabrescent loments, while the ]]>
Fig. 2). The shape of the articles, presence of distinct types of trichomes and aspects of epidermal cells, with epicuticular ridges and papillae, also proved to be useful in distinguishing among species (Fig. 1, Fig. 2, Fig. 3, Fig. 4, Fig. 5 y
Fig. 6).
The structural aspects of trichomes can be classified into uni-or multicellular and may still be simple, i.e., nonglandular or glandular. Five morphological types of trichomes were recognized and could be classified as follows: ]]>
1. Uncinate trichome (Fig. 3): glandular, with oil secretion at the base in all species. This trichome type showed dense distribution in D. adescendens, D. affine,
D. incanum, D. uncinatum, D. subsericeum and D. triarticulatum (Fig. 2A, Fig. 2B, Fig. 2E, Fig. 2I, Fig. 2K and Fig. 2L); however, they ]]>
Fig. 2C, Fig. 2D, Fig. 2F, Fig. 2G, Fig. 2H, Fig. 2J and Fig. 2M).
3. Globular unicellular trichome (Fig. 4L): glandular, secretion unspecified (non-oily and non-mucilaginous). This trichome type was only present in
D. uncinatum, and it showed no positive reaction to oil or mucilage. The substance could not be identified in this work.
4. Uniseriate trichome (Fig. 5): glandular, secretion throughout the structure. This trichome type was absent in D. subsecundum. When these trichomes were present, secreted oil was present in D. pachyrhizum, D. cuneatum and D. polygaloides, but ]]>
D. adescendens, D. affine, D. barbatum, D. leiocarpum, D. ]]>
, D. triarticulatum, D. tortuosum, D. subsecundum
and D. uncinatum.
5. Subulate trichome (Fig. 6): glandular, secretion (oil) at the base, when present. This trichome type occurs in D. barbatum, D. ]]>
D. cuneatum, D. subsecundum, D. leiocarpum and D. ]]>
Epicuticular wax depositions were found on D. pachyrhizum (Fig. 3J, Fig. 5I), D. polygaloides ]]>
Fig. 3K, Fig. 5G, Fig. 6D). D. uncinatum (Fig. 3H) and D. cuneatum (
Fig. 5H), while D. leiocarpum (Fig. 3G, Fig. 5D) showed the presence of epicuticular streaks on the epidermal surface. The epidermal cells in 9 of the 13 species were papillose, characterized by the convexity of the outer periclinal wall, which was more pronounced in D. affine (Fig. 3B) and D. triarticulatum (Fig. 3I, Fig. 5F), but also present in D. ]]>
(Fig. 3A), D. barbatum (Fig. 5C), D. subsecundum (Fig. 3E), D. ]]>
(Fig. 5D, Fig. 6E), D. subsericeum (Fig. 3M, Fig. 5K) and D. tortuosum
(Fig. 5J, Fig. 6C). In fruits of Desmodium, stomata were found on the fruit surface (Fig. 5B).
Discussion
The presence of trichomes on plants, as noted by Werker (2000), may serve as a mechanical barrier against various external factors, such as herbivores, pathogens, intense light, and temperature extremes. In the case of glandular trichomes, these structures can provide chemical protection to the plant by secreting substances, such as mucilage, ]]>
Uncinate trichomes were present in all species analyzed. Such hook-shaped trichomes play an important role in the dispersion of the diaspore by promoting fixation to the skin of ]]>
D. adscendens, D. affine, D. incanum, D. subsericeum, D. triarticulatum and D. ]]>
is epizoocoric since uncinate trichomes were more densely distributed on the fruit surface. However, in D. barbatum, D. cuneatum, D. pachyrhizum, D. polygaloides and D. ]]>
, the uncinate trichomes are sparse, indicating two forms of fruit dispersal: epizoocoric and anemocoric. For D. subsecundum and D. leiocarpum, ]]>
Desmodium present articles covered with uncinate trichomes, which make them suitable for epizoocoric dispersion; however, anemocoric dispersion is also observed in the genus. Moreover, according to Lima (2011), the ]]>
Globular multicellular trichomes were small in size and their presence could only be detected by optical or scanning ]]>
D. uncinatum.
Other surface features were observed in the epidermal ultrastructural ]]>
Epicuticular wax depositions were found on three species, including D. pachyrhizum, D. polygaloides and D. uncinatum. ]]>
D. ]]>
and D. leiocarpum showed epicuticular streaks on the epidermal surface, which is also related to xeric environ- ments and may, therefore, be complementary to the characterization of the species, but not a determinant of identification. According to Monteiro, Castro, and Giulietti (1985), the presence of epicuticular ornamentation can provide protection for ]]>
Desmodium, the presence of stomata may promote evaporation to maintain homeostasis of internal water supply in environments exposed to excessive solar irradiation.
The data on macro- ]]>
Desmodium species in Santa Catarina, Brazil. The following features were shown to be useful for the design ]]>
Acknowledgments
We ]]>
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1. Departamento de Botânica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina (UFSC), Campus Universitário, Florianópolis CEP 88040-900, Santa Catarina, Brasil and Herbário Barbosa Rodrigues (HBR), Av. Coronel Marcos Konder 800, Itajaí CEP 88301-302, Santa Catarina, Brasil; martinsf.daiane@gmail.com 2. Herbário Barbosa Rodrigues (HBR), Av. Coronel Marcos Konder 800, Itajaí CEP 88301-302, Santa Catarina, Brasil; ademir.reis.ufsc@gmail.com 3. Departamento de Engenharia Florestal, Centro de Ciências Agroveterinárias, Universidade do Estado de Santa Catarina (CAV-UDESC), Lages CEP 88520-000, Santa Catarina, Brasil; rosebortoluzzi@gmail.com 4. Departamento de Botânica, Centro de Ciências Biológicas, Universidade Federal de Santa Catarina (UFSC), Campus Universitário, Florianópolis CEP 88040-900, Santa Catarina, Brasil; marisa.santos@ufsc.br
Received 16-I-2014. Corrected 12-VII-2014. Accepted 14-VIII-2014.