Studies on the morphology and anatomy of vegetative organs of Cycas panzhihuaensis L. Zhou et S. Y. Yang

摘要

Cycas panzhihuaensis L. Zhou et S. Y. Yang is an ancient cycad, it is one of the wild cycads distributing in the farthest northern boundary, its morphology has a lot of special and primitive features and it is an important ring for study plant evolution (Fu et al., 1987; Zhou et al., 1981 & 1990). This paper reports the morphology and anatomy characters of the vegetative organs of Cycas panzhihuaensis. The results show the its root consists of two types: 1. Orthotropic roots grow geotropically with secondary growth, its primary root has diarch xylem, the rays of its vascular bundles consist of paratypic parenchyma cells; 2. Apogeotropic roots, namely coralloid roots. They have dichotomous branches and algal-band layer. The symbiotic algae belong to Nostoc or Anabaena. The stem is terete, seldom branched with pinnately compound leaves. Young leaves stayed in helical arrangement. The margins of the leaflets are flat. Its leaflets have a clear midrib, but no lateral veins. The stomata are monocyclic type. The vascular bundles of the midrib, petiolule and epicotyl all are ectophloic type. The tracheary elements of the metaxylem have many length-shortened, diameter-enlarged and oblique or vertical, end-walled bordered pit tracheids besides annular and helical ones.