Embryology of Swertia tetraptera Maxim. (Gentianaceae) and its systematic implication

Abstract

Abstract:

The embryology of Swertia tetraptera is reported for the first time. The anther

is tetrasporangiate and its wall, of which the development conforms to the dicotyledonous

type, is composed of epidermis, endothecium, middle layer and tapetum at the mature stage.

The tapetum has dual origin and is similar to the glandular type. Cytokinesis is of the simul-

taneous type and microspore tetrads are mostly tetrahedral. Pollen grains are mostly 3-celled

when shed. The ovary is bicarpellate and unilocular with four series of ovules. The fused

margins of two carpels intensively protrude into the locule. The ovule is unitegmic, tenuinu-

cellate and orthotropous. The development of embryo sac is of the Polygonum type. The de-

velopment of endosperm conforms to the nuclear type and the embryogeny corresponds with

the Physalis I variation of Solanad type. Three antipodal cells persist at the mature embryo

sac. The embryo is at the globular stage when seeds are released from the capsule. Compared

with the other studied species in Swertia, S. tetraptera shows differences from them in

three distinctive embryological traits: enlargement and protrusion of the fused margins of two

carpels into the ovary locule; orthotropous ovules and a developed hypostase. These three

characters were previously only found in the genus Halenia of the tribe Gentianinae in the

Gentianaceae,and thus suggest that S. tetraptera should be related to Halenia. The results

partly correspond with the molecular evidence (Yuan & Kupfer, 1995). The monophyletic

Halenia clade in Yuan & Kupfer's molecular cladogram includes Halenia, S. tetraptera

and Frasera (section Frasera in Swertia s. l.); nevertheless, up to now, no embryological

study on Frasera has been reported. The embryological results imply that the taxonomic sta-

tus of S. tetraptera needs to be revaluated and the genus Swertia s. l. may not be a mono-

phyletic group.

Key words: Swertia tetraptera, Embryology, Systematics

XUE Chun-Ying, HO Ting-Nong, LIU Jian-Quan. Embryology of Swertia tetraptera Maxim. (Gentianaceae) and its systematic implication[J]. .

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Embryology of Swertia tetraptera Maxim. (Gentianaceae) and its systematic implication

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