A Second Species of Aristogeitonia (Euphorbiaceae) for Tanzania

Abstract

the subfamily Phyllanthoideae; having imbricate tepals placed it in the tribe Phyllantheae, and compound leaves the subtribe Paivaeusinae. This subtribe, along with the subtribes Dissiliariinae and Toxicodendrinae, was subsequently made the foundation for a new subfamily, Oldfieldioideae (K6hler & Webster 1967), not only on account of foliar characters, but primarily because of the spiny pollen found throughout the group. Within that new subfamily, Aristogeitonia belongs to the subtribe Mischodontinae Mfill. Arg., characterized by having ? persistent epipetiolar stipules. However, its leaves are alternate, whereas those of the other genera of the subtribe are opposite. Apart from the first-described species, A. limoniifolia Prain, which is confined to Angola, and in which the large terminal leaflet is often accompanied by 1 2 smaller lateral leaflets, the other subsequently-described species seem to be consistently unifoliolate. In June 1995, Leonard Mwasumbi of the University of Dar-es-Salaam obtained some leafy shoots and fruits of an unmistakable new Aristogeitonia from the Pugu Forest Reserve only 23km SW of Dar-es-Salaam. The leaf-nervation pattern is somewhat different from that of other Aristogeitonia species in that the main lateral nerves tend to be more strongly and regularly developed, but the most obvious point of distinction is the nature of the stipules, which are large and foliaceous as opposed to being small and subulate to narrowly lanceolate. The fruits are similar to those of the other Tanzanian species, A. monophylla Airy Shaw (1972), except that the exocarp dehisces like the endocarp, i.e. septicidally, instead of independently of it, i.e. loculicidally; the fruiting pedicels in threes with the pedicel exceeding the columella in width are typical for the genus. As yet no male flowers have been collected. However, since these have not proved to be of especial significance hitherto in the taxonomy of the genus, I nonetheless decided to describe the novelty on the basis of fruiting material only, thus bringing the total number of species in the genus to five.