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1. chinaXiv:201707.00468 [pdf]

Studies on pollen morphology of selected species of Annonaceae from Thailand

Shao, Yunyun; Xu, Fengxia
Subjects: Biology >> Botany

The pollen morphology of 48 species and two varieties, representing 18 genera of the family Annonaceae from Thailand, is described and illustrated based on observations with scanning electron microscopy (SEM). The results reaffirm the great diversity in Annonaceae at the pollen morphological level, with the size of pollen varying from small, medium-sized to large, the shape of monads being elliptic, spheroidal or triangular with monosulcate, disulculate or no visible aperture, and the shape of tetrads being tetragonal, rhomboidal, tetrahedral, T-shaped or decussate. Ornamentation is echinate, psilate, microreticulate, rugulate, scabrate or verrucate. Decussate tetrads in Goniothalamus, and tetragonal, rhomboidal, T-shaped and decussate tetrads and new tetrad type in Mitrephora are first reported. The pollen grains of Anaxagorea show slightly bilateral and no visible aperture as a result of intine extrusion. The palynological evidence confirms the close relationship of Dasymaschalon, Desmos and Asian Friesodielsia, and shows the high diversity of pollen morphology within genera in Annonaceae.

submitted time 2017-07-13 Hits1878Downloads1039 Comment 0

2. chinaXiv:201707.00466 [pdf]

Floral development of monoecious Pseuduvaria trimera (Annonaceae) and comparative morphology and structure of its stamens and indehiscent staminodes

Yang, Guifang; Xu, Fengxia
Subjects: Biology >> Botany

Premise of research. Comparative development of staminate and pistillate flowers of Pseuduvaria trimera (Annonaceae) is firstly investigated to understand its sexual differentiation and developmental processes of flowers. Comparisons of morphological and anatomical features between mature stamens and staminodes are also described, in order to clarify the mode of anther dehiscence and understand the mechanism underlying the sterility of the staminodes. Methodology. Flowers at different developmental stages and mature stamens and staminodes were examined with SEM and light microscopy. Pivotal results. Flowers have complex whorled phyllotaxis as in other Annonaceae, with double positions in the outmost whorl of reproductive organs and variable stamen and carpel organ numbers per whorl. The stomium region of each theca is composed of the septum and stomium. The septum and stomium cells of stamens could be degenerated developmentally, facilitating anther opening, whereas those of staminodes maintain intact, forming indehiscent anthers. Conclusions. The developmental data suggest that staminate flower is unisexual from inception, while pistillate flower is morphologically hermaphroditic. The morphologically hermaphroditic flowers are nevertheless functionally pistillate as the anthers are indehiscent, and the structural andromonoecy of P. trimera actually functions as monoecy. The mechanism underlying the sterility of the indehiscent staminodes and delayed dehiscent outer stamens might be effective in promoting xenogamy. The occurrence of staminode is closely correlated with the acquisition and evolution of functional unisexual flowers in the genus Pseuduvaria.

submitted time 2017-07-13 Hits1489Downloads797 Comment 0

3. chinaXiv:201707.00079 [pdf]

Comparison of synandrium structure and development in three species from Myristicaceae

Yang, Guifang; Xu, Fengxia
Subjects: Biology >> Botany

Species of Myristicaceae have diverse and distinctive synandria morphology and structure, making them an interesting group for androecium evolution research. To clarify the morphology, structure, and origin of the synandrium, scanning electron microscopy and histology were performed on staminate inflorescences and flowers of Horsfieldia pandurifolia, H. tetratepala, and Myristica fragrans at different developmental stages. A whorl of stamen primordia was initiated rapidly around the margin of the floral apex in groups of two in H. pandurifolia and groups of three in M. fragrans. Each stamen primordium grew longitudinally, producing a pair of anther lobes and four microsporangia, accompanying one vascular bundle in H. pandurifolia and M. fragrans. In H. tetratepala, three stamen primordia groups were formed and each group with several anthers was supported by one vascular bundle, indicating a secondary increase of stamen. Three types of synandria origins were observed—in M. fragrans, the central sterile column tissues originated from the elongate receptacle; in H. pandurifolia and H. tetratepala, they were derived from a combination of floral meristem and fused connectives, and a combination of receptacular tissue and stamen groups. The diverse origins of the central sterile column suggest that the synandrium develops differently and independently in different genera and species of Myristicaceae.

submitted time 2017-07-12 Hits1229Downloads675 Comment 0

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