Nonglandular Trichomes of Californian and Hawaiian Tarweeds

Abstract

The purpose of this paper was to demonstrate the diversity in nonglandular trichome morphology of tarweeds at the ultrastructural level, and to propose categories for the morphologies reported for such trichomes. Using light and scanning electron microscopy (SEM), the authors surveyed 31 species of II genera of tarweeds from California and three genera of tarweeds from Hawaii. Trichome cell wall thickness in the Californian species ranged from I to 6 ~tm, whereas in the Hawaiian species trichome cell wall thickness ranged from I to 14 ~tm. Based on their surface appearance using SEM, trichomes were grouped into four categories: grooved; smooth + grooved; smooth; and verrucose.The verrucose surface of trichomes is an innate feature of the cell wall and is not due to resinlike deposits. The ecology and growth form of the plants in each group were compared to the trichome surface structure. Ecologically, members of the grooved group were alike in experiencing prolonged exposure to solar irradiation; eight of the nine plants in this group are perennial. The smooth + grooved group of trichomes was found on tarweeds that inhabit various types of habitats. This is likely a transitional group. The smooth trichome group is composed of mostly low-elevation Californian annuals. No Hawaiian tarweed surveyed had completely smooth trichomes. Tarweeds having verrucose-surfaced trichomes were mostly found in regions of moderate moisture. The trichomes observed in Dubautia platyphy/la were unique and could not be placed into any of the four groups; the surface of these trichomes was a combination of verrucose and smooth.

A Comprehensive Review on the Genus Plumbago With Focus on Plumbago Auriculata (Plumbaginaceae)

“…Non-glandular trichomes are also found occurring on the aerial vegetative parts of the plant as well as within plant tissue and can be described as follows (Fahn, 1988;Maclachlan and Carlquist, 1992): a) simple unicellular or multicellular, non flattened hairs; b) squamiform hairs which are conspicuously flattened, multicellular hairs. These trichomes are termed 'scales' if they are sessile or peltate hairs if they are stalked; c) branched, multicellular hairs which may be stellate; d) shaggy hairs which consist of a base and two or more contiguous rows of cells.…”