Vascular patterns in stems of the Cyclanthaceae

A survey was made of the distribution of stem vascular bundles in representatives of ten genera of the tropical monocotyledonous family Cyclanthaceae. Films of series of serial transverse sections were used to reconstruct the stem vasculature. Each leaf trace, followed in a basipetal direction from its level of insertion at the stem periphery, describes an obliquely downward course, initially contacting from 1 to 4 (or more) existing axial bundles. The associated bundles form a compound vascular bundle in which the original bundles initially remain discrete, most commonly in a tetrapolar arrangement, with four separate strands. Followed further in the basipetal direction, the strands eventually fuse partly or completely, usually to form a collateral or amphivasal axial bundle which participates in a new structural cycle. Quantitative variation between different taxa includes a simple patteIn in Ludovia, in which only bipolar bundles are developed. More elaborate forms have multipolar bundles with more than four separate strands. A systematically useful observation is that stem vasculature in Cyclanthus, representing the subfamily Cyclanthoideae, does not differ significantly from that in subfamily Carludovicoideae although there are some distinctive structural features. IN THIS PAPER we show that a distinctive pattern of organization of stem vasculature characterizes the Cyclanthaceae. The present study is part of a long-term effiort to understand the principles of stem vascular organization in monocotyledons. Our previous survey of the three-dimensional vasculature of the stems of the Araceae (French and Tomlinson, 1980, 1 9 8 1 a4, 1 9 8 3 ) provided general information about the internal organization of stem tissues for comparisons both within the family and with families like Pandanaceae, Palmae and Cyclanthaceae which have putative affinities. A summary of the results for the Araceae and some comparison with these groups is in preparation. Although comparable information about the Pandanaceae is given by Zimmermann, Tomlinson, and LeClaire (1974), and a summary of extensive observations on the palms is provided by Zimmermann and Tomlinson (1972, 1974; see also Zimmermann and Mattmuller, 1982), no detailed information on stem vasculature in the Cyclanthaceae is available (Harling, 1958). Therefore, the objective of this paper is to ' Received for publication 8 December 1982; revision accepted 24 March 1983. We gratefully acknowledge material supplied by Michael Madison (Marie Selby Botanic Gardens, Sarasota, FL) and George Wilder (Harvard Forest, Petersham, MA). Research supported by NSF Grant DEB 80-20726. 2 Present address: Department of Biological SciencesBotany, Rutgers University, P.O. Box 1059, Piscataway, NJ 08854. survey the three-dimensional organization of the Cyclanthaceae, using cinematographic methods that allow individual vascular bundles to be followed unequivocably for long distances in the stem. The same emphasis is used as in our previous survey of the Araceae, that is, to obtain an understanding of gross features at the generic level, rather than provide a detailed comparison of individual species. Of particular interest has been the recognition of the arrangement of vascular strands which become aggregated into "compound vascular bundles." The important point that three-dimensional analysis establishes is that the superficial similarity of compound bundles seen in transverse section is misleading, because a diversity of methods of aggregation can exist in diffierent families. In the Cyclanthaceae Harling (1958) recognized 11 genera in two subfamilies in a sequence followed in Table 1, which lists the species examined in the current study. Wilder (1978) regards one of Harling's genera, Pseudoludovia (monospecific), as of doubtful validity and probably based on a mixed collection. The largest genus is Asplundia (about 80 species), followed by Sphaeradenia and Dicranopygium (each with about 40 species). Stelestylis, Carludovica and Ludovia are small genera each with 3-4 species while Thoracocarpus, Evodianthus, Schultesiophytum and Cyclanthus are monotypic. Wilder (1977a, b, 1979, 1981 a, b) has recently added much to our understanding of architecture of the Cyclanthaceae and in par-