Stem vascular architecture in the rattan palm Calamus (Arecaceae–Calamoideae–Calaminae)1
P. Barry Tomlinson 2,5, Jack B. Fisher 3, Russell E. Spangler 4and Renee A. Richer 4
2Harvard Forest, Harvard University, Petersham, Massachusetts 01366 USA; 3Fairchild Tropical Garden, 11935 Old Cutler Road, Miami, Florida 33156 USA and Department of Biological Sciences, Florida International University, Miami, Florida 33199 USA; 4Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, Massachusetts 02138 USA
Received for publication March 21, 2000. Accepted for publication July 18, 2000.
Climbing stems in the rattan genus Calamus can reach lengths of well over 100 m, are long-lived, and yet their vascular tissue is entirely primary. Such a combination suggests that stem vasculature is efficient and resistant to hydraulic disruption. By means of an optical shuttle and video recording of sequential images we analyzed the stem of a cultivated species. The stem has vascular features that are unusual compared with those in arborescent palms and seemingly inefficient in terms of long-distance water transport. Axial bundles are discontinuous basally because leaf traces, when followed downwards, always end blindly below. Furthermore, there is no regular distal branching of each leaf trace at its level of departure into a leaf, so that neither a continuing axial bundle nor bridges to adjacent axial bundles are produced as in the standard palm construction. Instead, the axial bundles in the stem periphery are connected to leaf traces and to each other by narrow and irregular transverse or oblique commissures that are not the developmental homologues of bridges. As in other palms, metaxylem within a leaf trace is not continuous into the leaf so that the only connection to a leaf is via protoxylem. Within the stem, protoxylem (tracheids) and metaxylem (vessels) are never contiguous, unlike in other palms, which suggests that water can only move from metaxylem to protoxylem, and hence into the leaf, across a hydraulic resistance. We suggest that this minimizes cavitation of vessels and/or may be associated with an unknown mechanism that refills embolized vessels. Also, the metaxylem can be significant in stem water storage in the absence of abundant ground parenchyma.
Key Words: Arecaceae • Calamus • hydraulic architecture • liane • palm • rattan • vascular system • vessels
American Journal of Botany. 2001;88:797-809. © 2001 Botanical Society of America, Inc.