Structure and Symmetry of Species of the Asplundia Group (Cyclanthaceae) Having Monopodial Vegetative Axes: Schultesiophytum chorianthum, Dicranopygium Sp. Nov., Asplundia rigida, and Thoracocarpus bissectus

Abstract

Individual vegetative axes of S. chorianthum, D. sp. [an undescribed new species], A. rigida and T. bissectus have monopodial growth. Each adult leaf subtends a 1st-order lateral bud, that is either a vegetative bud, inflorescence bud or bud of uncertain nature (T. bissectus). Both 1st-order vegetative and inflorescence buds are borne intermittently on the vegetative axis; each sort of 1st-order bud may occur separately between 2 consecutively formed buds of the other type or in a group of 2 or more successively formed individuals. The prophyll of each 1st-order vegetative or inflorescence bud is a bicarinate scale leaf and is inserted above a very short hypodium. On 1st-order vegetative buds juvenile leaves always develop immediately distal to the prophyll. T. bissectus differs from the other 3 spp. in forming supernumerary buds which occur sporadically in either of 2 positions on basal portions of first-order lateral buds. In each species vegetative axes bear adventitious roots that form persistent root hairs and may branch. Adult leaves are always divided into lamina, petiole and sheath, but petiole development entails either differential growth (S. chorianthum, D. sp. and A. rigida) or both differential growth and tearing away of marginal portions of leaf (T. bissectus). Adult leaves always have open leaf sheaths and in D. sp. sheaths may terminate in small auricles (or stipules); in T. bissectus, on certain juvenile leaves of 1st-order, vegetative lateral buds and certain bracts on inflorescence peduncles (excluding prophylls in each case), the sheathing leaf base is consistently a closed structure. Inflorescence peduncles of all 4 spp. bear bracts which commonly subtend lateral buds of various higher orders of branching. On a 1st-order inflorescence, 1 or 2 of the most basally situated of these bracts may subtend from 1 (D. sp.) to 5 (S. chorianthum) higher-order, sometimes sympodially arranged inflorescences. Minute bracts, previously unreported on cyclanthaceous spadices, occur on spadices of S. chorianthum, D. sp. and T. bissectus; the bracts are considered vestigial, are most conspicuous in T. bissectus and in all 3 spp. are by far most obvious early in spadix development. It is uncertain whether bracts occur on spadices of A. rigida. All 4 spp. exhibit a substantial extent of mirror image symmetry.