J Syst Evol ›› 1996, Vol. 34 ›› Issue (6): 569-576.

• Research Articles • Previous Articles     Next Articles

Morphological Studies on Anastomoses and Blind Veins in Dichotomous Venation of the Leaf in Kingdonia uniflora

Ren Yi, Hu Zheng-hai   

  • Published:1996-11-10

Abstract: The morphology of the dichotomous venation,anastomoses and blind veins in the venation of the leaf of Kingdonia uniflora were studied in the present work. The laminan 5-divided. There are three veins at the base of the lamina,among which the middle one enters the base of the middle segment,and each lateral one dichotomyzes into two daughter veins. Each daughter vein enters the base of the lateral segments.The veins at the base of the segments dichotomize repeatedly 5~6 times forming the veins of different orders.Each vein of a particular order and its branches corresponde a particular lobe of the same order, and the ultimate vein terminates in the middle part of the umbo at the apex a tooth.In some cases,a vein in a lobe or a lobule dichotomizes and one of the daughter veins enters the lobe or lobule,but the other enters the neighbouring lobe or lobule.This kind of dichotome is named lobes-overstepped vein. One or two of the daughter veins can be blind veins with different lengths. The daughter veins overstepping the other lobe or lobule can form an anastomosis. The existence of the lobes-overstepped vein and the anastomosis formed by the overstepped daughter vein indicate that the venation of this monotypic genus is more complex than it was considered. Sometimes the two neighbouring veins of two lobes or lobules can be extremely approached and this is the approximate vein.There are two types of anastomoses in the venation of this species. No intermediate forms of the fusion of the vascular bundles were observed between the two completely fused veins of the anastomoses and thetwo separate veins of the approximate veins. But the vestige of different degrees of the commissural veins was observed. Therefore,we consider the formation of anastomosis from the approximate veins impossible. There are three types of blind veins in the venation of this species. The blind veins might have formed by the reduction of the vein terminating in a tooth accompanied by the reduction of the tooth, the interruption of the commissural veins of the anastomoses and the interruption of a veinlet from the branching point of a vein dichotome. According to the present morphological studies, we conclude that the dichotomous venation of the leaf of Kingdonia uniflora is of a characteristic of reduction and that the anastomosis is the vestige of the reduction from the closed venation to the open one. The occurrence of this kind of venation in the leaf of this species and some ferns and gymnosperms is a result of convergent evolution.

Key words: Kingdonia uniflora, dichotomous venation, anastomosis, blind vein, morphology