Beiträge zur Morphologie und Systematik der Klugieae und Loxonieae (Gesneriaceae): VI. Morphologie und Verwandtschaftsbeziehungen von Loxonia und Stauranthera

Abstract

Summary A new interpretation of the shoot and inflorescence structure of the two markedly anisophyllous genera Loxonia and Stauranthera is presented. Loxonia: Up to now the inflorescences have been believed to arise from the axils of the minor leaves and to represent morphologically “partial florescences”. This interpretation is incorrect: they are strictly terminal (but usually curved down) and must be regarded as complex structures: “florescences” (sensu Troll) composed of some few partial florescences arising from the axils of small bracts. The partial florescences are either “pair-flowered” (L. discolor, L. burttiana) or “normal” cymes (L. hirsuta). Their alternative arrangement within the florescence is, in accordance with the general anisophyllous shoot organization, a result of differentiation of the (isophyllous) bract pairs into “ + ” and “–” bracts and only the “+” ones being fertile. – Consequently, the whole floral region of the plant (resp. of a branch) is to be regarded as a sympodium of shoot segments, each of which consists of an anisophyllous leaf pair and the florescence. The consecutive shoot segments arise exclusively from the axils of the major leaves. In this way a highly complex synflorescence, a “polytelic anthocladium”, is formed. Stauranthera exhibits a similar organization. However, the number of shoot segments is low and their development apparently depends on nutritive conditions. The “inflorescences” can be pure florescences as in Loxonia or synflorescences by substitution of the lowest partial florescence by a co-florescence. The peculiar shoot and inflorescence structure as well as anatomical and flower characters allow the conclusion that Loxonia and Stauranthera are fairly closely related and that they are derived from a Whytockia- like ancestor. It is also suspected that a somewhat close affinity exists between these two genera and Epithema (as well as Rhynchoglossum).