Notes on Amaranthaceae: 2

Abstract

Summary. Within the genus Aerva, the sexual and other diversity of A. lanata (L.) Juss. ex Schultes and A. leucura Moq. is discussed, A. sansibarica Suesseng. and A. incana Suesseng. being reduced to the synonym of A. lanata; variation in A. javanica (Burm. f.) Juss. ex Schultes var. bovei Webb is also discussed. Aerva curtisii Oliv. and A. cochinchinensis Gagnep. are transferred to a new genus Psilotrichopsis, and A. monsoniae Linn. f. to a new genus Trichurus. Psilotrichum is revised in SE. Asia. Pupalia orbiculata Heyne ex Wall. becomes a variety of P. lappacea (L.) Juss. The relationships of Digera Forssk.. Neocentema Schinz and Pleuropteranthera Franchet are dealt with; finally, Amaranthus dubius Mart. ex Thell., A. lividus L. and Centrostachys aquatica (R.Br.) Wall. ex Moq. are typified. A new varietal combination is made for what has previously been thought to be the 'typical' variety of Achyranthes aspera L., and for two other varieties of this species. Aerva lanata (L.) Juss. ex Schultes and A. leucura Moq. A. leucura Moq. has been maintained as a species distinct from A. lanata for the 'Flora of Tropical East Africa' account as it stands at the moment. This reflects no great conviction that such is the true state of affairs, but rather that even after protracted study I find that I have nothing of significance to add to our knowledge of the taxonomy of these two plants. As Hauman (1951: 59) remarks, A. leucura is an ill-defined and unconvincing species, comprising as it does plants which resemble a paniculate variety of A. lanata, and identical with the latter in flowers, fruit and seed. Were the two wholly sympatric with numerous intermediates, one would unhesitatingly subordinate A. leucura as a variety of A. lanata. However, while A. lanata ranges through most of tropical Africa to South Africa (where, however, it appears to be rare) and thence from Arabia eastwards through tropical Asia to the Philippines and New Guinea, A. leucura is confined to Africa southwards from Uganda and Kenya (one rather atypical specimen only seen from the latter country) to South Africa, where it is common. Similarly, even within the F.T.E.A. range A. leucura is, if one may judge from herbarium material, much more restricted in altitude range than A. lanata, scarcely descending below 6o00 m, while A. lanata occurs commonly at sea level. It would perhaps be fashionable to make a subspecies of A. leucura-a course of action which would merely create a new binomial to no profit; for the moment, it seems best to continue to regard these two as vicarious species. Such intermediates as occur are chiefly found in the area where the two plants overlap in abundance (e.g. in Tanzania), and may as well be due to hybridization as to any other course. Genetical investigation is much needed here. As well as being a troublesome genus taxonomically the sexuality of Aerva appears complex. The widespread A. javanica (Burm. f.) Juss. ex Schult. seems to be constantly dioecious; conversely, all the material which I have examined of the Indian A. sanguinolenta (L.) Bl. (A. scandens Roxb.) has had well-developed anthers and stigmas, though Backer (1949: 85) describes it as having flowers hermaphrodite or female. But in A. lanata there is a more involved situation. In the Flora Malesiana region it is, according to Backer,