The morphology of some species of cheilanthes

Abstract

Morphology of ten species of Cheilanthes is studied and a phylogenetical evaluation of the data attempted. The vascular cylinder of the rhizome is dictyostelic with prominently overlapping, spirally arranged leaf gaps and simple, gutter-shaped leaf traces. The branch trace is cylindrical and unaccompanied by any branch gap. The stipe bundle is single, but the xylem tissue is split into two ribbon-like bands, which, towards the apex of the stipe, unite together at their metaxylem regions, forming a characteristic solid strand bearing pairs of adaxial and abaxial ridges. Paleae and hairs occur on the leaf lamina. In some species, small glandular hairs on the leaf secrete a waxy substance which forms a characteristic silvery or golden crust. Sporangia are few per sorus and seated at the tips of veinlets towards the leaf margin and protected either by infolding of the margin beyond the sorus or, more commonly, by a scarious indusium. The sporangia are massive, usually short-stalked and with the wall composed of a large number of small chloro-phyllous cells. Spores vary from smooth-walled types with crassimarginate laesurae and thin exine to globose with highly ornamented thick exine and tenuimarginate laesurae. The prothalli are cordate, naked, developing through the activity of an obconical apical cell which is later replaced by a marginal multicellular meristem, and in many species possessing collenchyma-like thickenings of the wing cells. The juvenile leaf is simple, with a more or less entire, spatulate lamina and dichotomous veins. A midrib is established early. Small glandular hairs occur all over juvenile lamina, especially towards the margins.