The character states of Mussaendopsis Baill. (Rubiaceae-Coptosapelteae)

Abstract

Summary Mussaendopsis, an arborescent Southeast Asiatic genus of two species (M. beccariana: from the Malay Peninsula and Sumatra East to Borneo; M. celebica: endemic to Sulawesi) has mature stipules in an intrapetiolar position. Developmental studies on M. beccariana, however, showed that they are initially interpetiolar. The large coriaceous leaves, characterized by the presence of two hypodermis layers, have conspicuous sclerenchymatic bundle sheath extensions. The optical attractiveness of the (pleio-)thyrsic or thyrsopaniculate, axillary inflorescences is markedly increased by the presence of enlarged, petaloid, show calyx lobes which are produced only by certain flowers of an inflorescence (± pseudanthium-like). The corollas (corolla lobe aestivation contorted to the right in bud) differ significantly in the two species: In M. celebica, they are hypocrateriform (corolla tubes c. 3.5 mm long; tubes always shorter than the lobes) and in M. beccariana, they are rotate (tube subobsolete to obsolete). The latter, suspected to be myophilous (“dishblossom”, large, exposed ± flat disk profusely producing nectar), shows dichogamy (protandry) coupled with herkogamy. The ovary of the bicarpellate gynoecium contains two large placentas, each with numerous hemianatropous, tenuinucellate and unitegmic ovules which are produced in a sequential fashion. In the course of flower and fruit development, ovules and developing seeds undergo a drastic change in shape: ovules soon develop a winglike extension (marked elongation of the chalazal region!), resulting in a distinctly imbricate arrangement of the tightly packed, variably shaped ovules. Further on, the wing-like outgrowths also encompass the micropylar end of the ovules so that, finally, the mature seeds show an elongated, bipolar wing which surrounds the ± centrally located endosperm- and embryo-bearing part on all sides. The exotesta cells have conspicuous anastomosing local secondary thickenings on the inner tangential walls only. The distinctly oily endosperm consists only of a few cell layers surrounding the relatively large embryo. The fruits are septicidal capsules with hard walls (thick, sclerenchymatic endocarp). The pollen of M. beccariana, 3-colporate and ± spheroidal (P = ± E = 18 – 19.8 μm), has a reticulate to finely reticulate exine. The presented data do not seem to seriously contradict the recently suggested placement of Mussaendopsis in the tribe Coptosapelteae, although they might suggest a ± isolated position of the genus in this essentially paleo tropical tribe.