Microsporogenesis and Male Gametogenesis of Thymus quinquecostatus

Purposes In the present investigation, we aimed to accumulate embryological data of Lamiaceae, to provide embrilological evidence on clarification of the systematic position of Thymus, and to provide base data on the introduction and cultivation of Thymus quinquecostatus.

Methods Conventional paraffin method was used.

Results Each anther has four sporangia. Development of the anther wall belongs to the dicotyledonous type and the anther wall comprises of epidermis, endothecium, one middle layer, and the tapetum. The cell wall of endothecium and part of connective tissue cells have fibrous thickening. The cells of glandular tapetum were 2-nucleate. Cytokinesis of the microspore mother cell is simultaneous, resulting in the tetrahedral tetrad. The mature pollen grain is 3-celled and hexacolpate. Pollen abortion is common.

Conclusions The characteristics of microsporogenesis and male gametogenesis of T. quinquecostatus, especially the 3-celled and hexacolpate mature pollen grain support moving Thymus from Lamioideae to Nepetoideae in molecular systematic classifications. Pollen abortion maybe is one of the factors leading to low seed setting rate.