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The unique fl oral morphology of the South African orchid H. pulchra , with its twin meranthia, is best explained as an adaptation to pollination by oil-collecting bees. Flowers consisting of meranthia (fl oral parts that function as single pollination units; commonly observed in garden Iris ) are extremely rare among the angiosperms and their signifi cance poorly understood. Unlike all other known examples of meranthia, the novel type described for H. pulchra is not bilabiate. All Huttonaea species are unique in having twin petal sacs with glandular verrucae that secrete oil and are pollinated by Rediviva (Melittidae) oil-collecting bees. But only Huttonaea pulchra has long and widely divergent petal claws that place the oil sacs well beyond the reach of a centrally positioned bee. The wide separation of these sacs forces the pollinator, R. colorata , to visit each side of the fl ower independently and effectively divides the fl ower into two meranthia. Molecular data indicate that the evolution of the Huttonaea -type meranthium was dependent on the prior evolution of the oil fl ower/oil bee relationship. Meranthium evolution was also facilitated by the presence of oil in two separate structures (petal sacs) that were not physically constrained to remain in close proximity.

The subtribal delimitation and relationships of Orchideae remain unresolved. In the present study, the phylogenetic relationships among all subtribes of Orchideae were reconstructed, utilizing five plastid and two nuclear DNA sequences ( rbcL , trnS - trnG , matK , trnL - F , psbA - trnH , Xdh and ITS) from 178 taxa of Orchideae. The combined results show that most clades are successively sister to the grade of clades representing antecedently accepted subtribes, but Pachites and Huttonaea do not belong to the previous classification of Disinae. In contrast, these two genera represent two additional isolated lineages. On this basis, a new subtribe, Pachitinae, is tentatively proposed to accommodate this taxon. Also, the subtribe Huttonaeinae Schltr. was recovered (1926: 568). In addition to the taxonomic treatment of this subtribe, the delimitation of many related subtribes in Orchideae is discussed.

The development, final appearance and digestion (during germination) of seed reserves in a number of genera of the Orchidaceae (tribe Orchideae) has been studied comprehensively, using ultrastructural and histochemical techniques complemented by gas chromatographic analysis of free sugars. Mature seeds of Disa, Disperis and Huttonaea contain substantial reserves of lipid and protein in the embryo. The protodermal cells of Disperis also contain protein-carbohydrate bodies. Free sugars are present but starch occurs only in immature seeds. Glyoxysomes are absent and lipolysis does not occur in seeds incubated without an external source of sucrose, and although a little starch is formed it is apparently synthesised from endogenous sucrose reserves. In the presence of exogenous sucrose, however, proteins are hydrolysed and glyoxysomes appear. Substantial quantities of starch are formed in such seeds. From these observations it is apparent that orchid seeds are unable to utilise endogenous reserves of lipid unless simple sugars are supplied to the medium but can utilise the free sugars present in the embryo. Resultant conclusions on the role of mycorrhizae in the germination of orchid seeds are discussed.