Steganthera
Content
Description
Trees or shrubs, resting buds with cataphylls.
Monoecious or dioecious.
Leaves pubescent at first, sometimes becoming glabrous, entire or dentate, principal secondary veins arched and meeting within the margin.
Inflorescences later-al, cymose or fasciculate.
Distribution
Asia-Tropical: Bismarck Archipelago (Bismarck Archipelago present); Maluku (Maluku present); New Guinea present; Sulawesi (Sulawesi present), Australasia: Queensland (Queensland present), Solomons present
Queensland, Solomons and Malesia: Celebes, Moluccas, New Guinea (incl. Bismarck Archipelago).
Notes
Steganthera is frequently confused with Kibara, another common and widely distributed genus, because the foliage, fruits and inflorescences are similar. The technical differences between these two genera are not readily observable. They are, firstly, the greater number of tepals in Kibara, certain of which are thickened and glandular in the female receptacle, and, secondly, the greater number of stamens in the androecium (but see S. salomonensis). However, other features usually allow a generic identification to be made. The most important of these is the appearance of the pedicel: in Steganthera the pedicel is relatively slender and is clearly distinct from the receptacle, whereas in Kibara the pedicel is thickened distally and has a less clearly defined junction with the receptacle or none at all. Another useful indication is that the leaves usually dry greenish (often yellowish green) in Kibara, whereas in Steganthera they are mostly brown when dry.
The species of Steganthera can be placed in three groups on morphological grounds. One is characterized by the expansion of the female, and to a lesser extent also the male flower, into a turbinate or patelliform receptacle. This group formerly was segregated as the genus Anthobembix, but KANEHIRA & HATUSIMA () set out valid reasons for uniting the two genera. A second group of species is characterized by their fasciculate inflorescences and by being dioecious. The third group comprises those species lacking both these characters; that is, the species have subglobose receptacles in cymose inflorescences. It includes a number of species which are difficult to separate, including S. hirsuta which is very variable in all its characters. The species of the first two groups are well defined morphologically and geographically, where-as those of the third group form a complex which has not yet resolved itself into stable species. These three groups of species are not given formal taxonomic recognition because their limits are not clearly defined. Steganthera dentata and S. cyclopensis combine fasciculate inflorescences with discoid receptacles and therefore fall into both of the first two groups. In some species the expansion of the receptacle is a variable character; for example, in 5. hospitans and S. oligantha the male flower may be globose, but this may be due to hybridity with S. hirsuta.
The association of some species with ants is very striking. These species have enlarged nodes with well-defined pores leading into the hollow stems. Scale insects line the pith cavities and small black ants abound over the plant surface and in the hollow stems. The association is most conspicuous in the large-leaved and abundant species S. hospitans, but also occurs in S. moszkowskii, S. ledermannii and S. royenii.
Pollination biology has not been studied and the structure of the receptacles poses several problems. The male receptacles have open, if small, ostioles at the time the anthers dehisce, but it is not known what insects visit them. The carpels in the female receptacles are covered by the 'calyptra' at anthesis. The ostiole giving access to the female receptacle is even smaller than that of the male and it is not known how pollen reaches the stigmas. These are awl-shaped and converge towards the ostiole. In Kibara and some other genera pollen is received on a hypostigma outside the receptacle () but this is not so in Steganthera.
The species of Steganthera can be placed in three groups on morphological grounds. One is characterized by the expansion of the female, and to a lesser extent also the male flower, into a turbinate or patelliform receptacle. This group formerly was segregated as the genus Anthobembix, but KANEHIRA & HATUSIMA () set out valid reasons for uniting the two genera. A second group of species is characterized by their fasciculate inflorescences and by being dioecious. The third group comprises those species lacking both these characters; that is, the species have subglobose receptacles in cymose inflorescences. It includes a number of species which are difficult to separate, including S. hirsuta which is very variable in all its characters. The species of the first two groups are well defined morphologically and geographically, where-as those of the third group form a complex which has not yet resolved itself into stable species. These three groups of species are not given formal taxonomic recognition because their limits are not clearly defined. Steganthera dentata and S. cyclopensis combine fasciculate inflorescences with discoid receptacles and therefore fall into both of the first two groups. In some species the expansion of the receptacle is a variable character; for example, in 5. hospitans and S. oligantha the male flower may be globose, but this may be due to hybridity with S. hirsuta.
The association of some species with ants is very striking. These species have enlarged nodes with well-defined pores leading into the hollow stems. Scale insects line the pith cavities and small black ants abound over the plant surface and in the hollow stems. The association is most conspicuous in the large-leaved and abundant species S. hospitans, but also occurs in S. moszkowskii, S. ledermannii and S. royenii.
Pollination biology has not been studied and the structure of the receptacles poses several problems. The male receptacles have open, if small, ostioles at the time the anthers dehisce, but it is not known what insects visit them. The carpels in the female receptacles are covered by the 'calyptra' at anthesis. The ostiole giving access to the female receptacle is even smaller than that of the male and it is not known how pollen reaches the stigmas. These are awl-shaped and converge towards the ostiole. In Kibara and some other genera pollen is received on a hypostigma outside the receptacle () but this is not so in Steganthera.