An account of the Papuasian species of Calamus (Arecaceae) with paired fruit

Summary: A taxonomy is proposed for Papuasian species of Calamus (Arecaceae) in which the fruits are borne in pairs, rather than singly. Five species are recognised. Calamus pholidostachysJ. Dransf. & W. J. Baker is described as new, C. macrospadix Burret is reduced to synonymy with C. macrochlamys Becc., C. steenisii Furtado and C. laceratus Burret are both reduced to synonymy with C. zebrinus Becc., C. altiscandens Burret is accepted and the until now poorly known C. fertilis Becc. is fully described for the first time. The subject of this paper is a group of five Papuasian species of Calamus in which the pistillate flower-bearing branches (rachillae) are unusual in carrying flowers in groups of three or four, rather than in pairs as in most species. Fruits are, consequently, often borne in pairs. In subfamily Calamoideae (Arecaceae) the arrangement of flowers within flower clusters conforms to precise patterns. These patterns have been taxonomically important in the grouping of genera into subtribes in palm classification (Dransfield & Uhl 1986; Uhl & Dransfield 1987; Baker et al. 1999, 2000). While the formal classification of the Calamoideae of Dransfield & Uhl (1986) has been refined and superseded by that of Baker et al. (2000), the architecture of the flower clusters remains an important morphological character in the definition of genera and of suprageneric groupings. Within the Calaminae almost all genera and species display dyads in the pistillate inflorescence. The dyad is a sympodial unit (Uhl & Dransfield 1987), a cincinnus consisting of two flowers and two bracteoles borne in the axil of a rachilla bract; in the Calaminae, dyads in the pistillate inflorescence consist of a terminal, sterile staminate flower that also bears a bracteole, in the axil of which is a fertile pistillate flower, it too bearing a bracteole (Fig. 1B). Crowding and adnation frequently obscure the relationship of bracts to flowers, but examination of young stages clearly shows the sympodial nature of the dyad (Dransfield 1970). In the staminate inflorescence the flowers are borne singly, each in the axil of a rachilla bract and together with a bracteole (Fig. 1A). In the Calaminae there are a few exceptions to this precise arrangement. In the genus Retispatha, sterile staminate flowers are almost consistently lacking from the pistillate inflorescence, although the presence of two bracteoles per pistillate flower indicates that the pistillate flower is in a lateral position; a sterile staminate flower has been found once in one specimen (Uhl & Dransfield 1987). In a few abnormal individuals within species of