Pleuropetalum darwinii Hook. F. is still an anomalous member of Amaranthaceae Juss. An embryological evidenceстатья

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[1] Veselova T. D., Timonin A. C. Pleuropetalum darwinii hook. f. is still an anomalous member of amaranthaceae juss. an embryological evidence // Wulfenia. — 2009. — Vol. 16. — P. 99–116. The present investigation was aimed at revealing embryological characters of Pleuropetalum, a 'problem' member of Amaranthaceae, and elucidating affinities of this genus. Rather many embryological traits are shared by Pleuropetalum as well as by core Amaranthaceae. Most of these traits, however, are also inherent in the vast circle of centrosperms outside the family Amaranthaceae. Pleuropetalum contrasts with core Amaranthaceae but resembles some members of the closely related Portulacaceae and Cactaceae in exotesta structure. Contrary to stalactiform thickenings of the outer cell walls of the exotestal cells - which are typical of Amaranthaceae - such walls in Pleuropetalum are evenly thick, show a gradated staining and are penetrated by polysaccharide dendrites and numerous pore channels just like the ones in some Portulacaceae and Cactaceae. Pleuropetalum also differs from core members of Amaranthaceae in having aleuron grains and lipid globules in its embryo cells and thus is similar to representatives of Portulacaceae, even Didiereaceae, and Caryophyllaceae. Pleuropetalum is strikingly similar to Amaranthaceae in its multiseriate anther archesporium, whereas the anther archesporium of Portulacaceae is always uniseriate. Calcium oxalate crystals in pollen are a character shared by Pleuropetalum and some Phytolaccaceae. Such crystals have not been revealed in core Amaranthaceae so far. Pleuropetalum differs from Phytolaccaceae in a much thinner nucellar cap, invariably 2-layered integuments with an air chamber in between, and neither placental nor funicular obturators. Seemingly unique traits of Pleuropetalum are (i) an exostome which supersedes the endostome after legitimate fertilization, (ii) an exudate that precipitates to plug the micropyle of the unfertilized ovule, and (iii) aleuron grains and protein crystals as reserve material in perisperm cells. It's concluded from our new embryological data that Pleuropetalum is even more a 'problem member' of Amaranthaceae than it has been supposed before. Keywords: Pleuropetalum, Amaranthaceae, embryology, anther, ovule, archesporium, microsporogenesis, megasporogenesis, embryo sac, embryo, seed coat.

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