J Syst Evol ›› 1996, Vol. 34 ›› Issue (6): 577-585.

• Research Articles • Previous Articles     Next Articles

The Embryological Studies of Comastoma pulmonarium (Gentianaceae)

Liu Jian-quan, Ho Ting-nong   

  • Published:1996-11-10

Abstract: This paper describes embryological characters of Comastoma pulmonarium(Turcz.)Toyokuni for the first time,with an aim of discussing the systematic position of the genus Comastoma.The development of anther walls conforms to the dicotyledonous type.All tapetum cells origin from the primary parietal cells.The tapetum with uninucleate cells is of secretory type.The epidermis persists while endothecium degenerates.Cytokinesis in the microsporocyte meiosis is of simultaneous type and microspore tetrads are tetrahedral.Pollen grains are 3-celled.The ovary is bicarpellate,unilocular with eight series of ovules and typical with parietal placentation.The ovule is unitegmic,tenuinucellate and anatropous.Ihe embryo sac originates from a single-cell archesporium.The chalazal megaspore in linear tetrad is the functional one.The development of embryo sac is of the Polygonum type.Before fertilization,two polar nuclei fuse into a secondary nucleus.Three antipodal cells persist while divide into 8-12 cells,each of which is multiseriate containing more than 3 nuclei.The size of the antipodal cell is enlarged to be several times bigger than the normal cell.The haustorium formed from antipodal cells is distinct.Fertilization is porogamous.The pollen tube destroys a synergid to enter embryo sac and discharge the two sperms.One of the sperms fuses with the egg cell to form the zygote while the other with the scondary nucleus to form the primary endosperm nucleus almost simultaneously.The fertilization conforms to premitotic syngamy type.The development of the endosperm is of the Nuclear type.The early several divisions of the endosperm nuclei are simultaneous and each nucleus contains 2~3 nucleoli. The embryogeny corresponds to the Physalis I variation type the Soland type.The antipodal cells form a layer of“out endosperm”just out of the endosperm nucleus layer and degenerate after the division of the zygote.Compared with Gentiana,Gentianella and Lomatogonium,Comastoma is embryologically more closely related to Gentianella than to Gentiana and Lomatogonium.It shares more embryological similarities with Gentianella than the other two genera,but differs from Gentianella in some important characters such as ovule curvature,ovule series,placentation and the path of pollen tube.However,these diagnostic characters are usually used to circumscribe the taxon above the generic rank.Therefore,from embryological evidence,Comastoma is better bestowed as a generic rank.This genus is more primitive than Gentianella according to evolutionary trends of the embryological characters.

Key words: Comastoma, embryology, taxonomy, systemtics