Mabea

Authority

Maguire, Bassett. 1967. The botany of the Guayana Highland--Part VII. Mem. New York Bot. Gard. 17: 1-439.

Family

Euphorbiaceae

Scientific Name

Mabea

Description

Genus Description - Mabea is a sharply circumscribed genus. It is best distinguished from all other genera of Hippomaneae by the long style, the long undivided stigmas, and the composition of its inflorescence, which can be described as a thyrse. The main axis (rhachis) bears a great number (30-60) of secondary inflorescences, consisting of the male cymules and in its basal portion a few (1-4) female flowers which do not aggregate into cymules, but are individually located on the rachis. In contrast to the clarity and ease with which the genus can be circumscribed, the species within the genus are difficult to segregate. Bentham’s statement made in 1880 still holds: "genus naturalissimum vix in sectiones dividendum." Pax and K. Hoffmann in 1912 attempted to subdivide Mabea into 4 sections based on the presence or absence of glands on one of the female sepals, on the degree to which the pedicels are connate in the cymules and on the number of stamens per male flower. Apart from the difficulty of counting the sessile stamens congested on the thorus, all of these characters are variable even in the flowers of the same tree. The male cymules in the great majority of cases consist of 3 flowers, the central one best developed, borne on a slightly longer pedicel and bearing most stamens, the two lateral ones with less stamens and shorter pedicels. If the pedicels are connate at the base, and connation is at the same level, the cyme is referred to as an umbel; if free to the base it is called a ternate fascicle. This general pattern deviates in two directions: cymules with more than 3 flowers, and cymules reduced to two or one flower (M. linearif olia). Mabea sect Spiculigerae Pax & K. Hoffm. is characterized by having more than 3 flowers per cymule, and by the variety of pattern of connation of the pedicels. This is often raceme-like, with one flower on a central longest pedicel, and the lateral flowers attached at various levels. This section, while the best defined and geographically limited to the Peruvian and Bolivian Andes and central Brazil, is considered the most primitive one. It does not occur in the Guayana Highland. At the base of the male cymule there is one small bract with two often very conspicuous glands. This bract together with its two glands is often elevated high above the rachis on a subbracteal peduncle. The extreme deviation of the general pattern in another direction, exemplified by M. frutescens, M. orbiculata and M. linearifolia together with the Peruvian M. elegans, is characterized by the greatly reduced male cymules, and a low shrubby growth.

Distribution and Ecology - Mabea is confined to tropical America. Its geographical center of development is in the Amazon Valley, from where it spreads in different directions; northward and along the Andes as far north as Guatemala and southern Mexico, southward as far as Yungas, Bolivia and Rio de Janeiro. It is missing in the West Indies (except Trinidad). Of the 51 species of Mabea recognized today, 18 occur in the Guayana area. Of these M. nitida and M. eximia are found also in the Amazon Valley; M. occidentalis and M. parvifolia are widespread also in the Andean and sub-Andean belt. Of the remaining 33 species which do not occur in the Guayana Highland and are not treated here, 12 are confined to the Andean and sub-Andean belt, 10 to the Amazon Valley, and the remaining 11 belong to central Brazil. Species of Mabea are handsome, wind-pollinated trees, shrubs or lianas and are typical representatives of the river-shore vegetation. They are frequently found at lower altitudes between 50-400 m, but a few attain higher altitudes. The highest recorded altitudes to which they reach are 1065-1220 m; M. caudata, M. parguazae and M. schomburgkii; 900 m: M. rubicunda and M. saramaeeensis; 850 m: M. taquari, M. eximia, M. argutissima and M. occidentalis; and 663 m: M. piriri. Of the 18 species discussed below, 7 are new; for 4 of the remainder (M. argutissima, M. saramaeeensis, M. nitida and M. eximia) types were available; 3 types (M. caudata, M. schomburgkii and M. piriri) are known only from photographs; the identification of the remaining 4 types (M. biglandulosa, M. occidentalis, M. taquari and M. parvijolia) had to rely on description alone. Three names, M. pulcherrima, M. costata and M. subserndata are suspected earlier synonyms, but since types were not available and the descriptions are inadequate, the more recent and well typified names, M. argutissima and M. exim ia, were used. The key given below is a compromise between an artificial key and one expressing natural relationships.

Discussion

Type. M. piriri Aubl.