A Biological Study Of Excentrodendron Hsienmu H.T. Chang And R.H. Miau And Its Significance In Conservation Ecology

Excentrodendron hsienmu (W. Y. Chun and F. C. How) H. T. Chang and R. H. Miau (Malvaceae s.l.) is a typical and usually a co-dominant tree species in limestone montane rainforests. It is restricted in southwestern Guangxi and southeastern Yunnan of China, North Vietnam and Laos.Segregation of Excentrodendron from Burretiondendron has hardly been accepted despite their distinct pollen morphology and wood anatomy. Microsporogenesis, microgametogenesis, megasporogenesis andmegagametogenesis were studied in E. hsienmu and Burretiondendron esquirolii in order to examine the basis of segregation of Excentrondendron from Burretiodendron and to study the affinity of Excentrodendron.Flowers of E. hsienmu did not blossom every year though large numbers of flower buds developed. Male trees bear a compound cyme of 3-12 and female trees mostly solitary flower or rarely a cyme of 2 flowers. Staminate flowers and pistillate flowers were similar in size, with 3 epicalyxes, 5 sepals with basal nectary, and 5 petals.Each 5-6 stamens of the fertile staminate flower are connate at the base, forming 5 clusters. Stamens 25-30. Anther is two-locular and tetrasporangiate. Single archesporium differentiates beneath the epidermal cells. Four to six niicrosporocytes are seen on the transverse section of the anthers and only 1-3 develop into functional microspore mother cells. Cytokinesis is simultaneous and the microspore tetrads are...