Pollen morphological studies in tribe ocimeae (Nepetoideae: Labiatae): I. Ocimum L.

Abstract

The pollen of 20 species, 53 collections, of Ocimum and 6 species from 4 closely allied genera: Becium Lindl., Dauphinea Hedge, Erythrochlamys Guerke and Orthosiphon Benth. was acetolysed and examined with light, scanning electron and transmission electron microscopy. Four pollen types are described, three are subdivided. Keys are provided to the types and subtypes. Results show some notable parallels with taxonomic opinion. A number of examples are cited in which the pollen morphology supports recent or proposed taxonomic changes, for example the transfer of Erythrochlamys cufodontii Lanza and E. nummularia (S. Moore) Hedge to Ocimum, of Ocimum hanningtonii Baker to Orthosiphon and of both Ocimum irvinei J. K. Morton and O. urundinense Robyns & Lebrun to Becium. Parallels with pollen types are drawn between Old and New World species; Pollen Type I occurs in both the Old and New Worlds while Pollen Types II, III and IV are exclusively Old World. Data from geographic distribution and pollen morphology suggest that Pollen Type I is the basal type for Ocimum. A previously unexploited character, presence or absence of mucilage on the nutlets of different species is compared with the distribution of pollen types within Ocimum. Presence of mucilage is particularly associated with Pollen Type II (A, B) species which comprise section Ocimum subsection Ocimum. Mucilage is also noted on the nutlets of the only two New World species in the present study which have been examined for this character, both species have pollen of Type IA. Summary tables are provided for comparative data. © 1992, Taylor & Francis Group, LLC.