Asteropollis

Stamen with Asteropollis - type pollen sp. 2

Text-fig. 15a–e

D e s c r i p t i o n a n d r e m a r k s. The species is based on a single stamen with numerous Asteropollis- type pollen grains in situ. The stamen is about 0.9 mm long and 0.4 mm broad, obovate in shape, with a pointed base and a domeshaped sterile extension of the connective with short, stiff trichomes at the apex (Text-fig. 15a). There are no remains of a filament and the anthers may have been sessile or almost sessile. The anther is tetrasporangiate with two pairs of pollen sacs (Text-fig. 15a). Pollen is pentachotomocolpate, rarely tetrachotomocolpate, circular in equatorial outline and about 15–18 µm in diameter (Text-fig. 15b–d). The arms of the aperture are short and do not reach to the equator. The aperture margins are poorly defined and the aperture membrane is covered by irregular verrucae (Text-fig. 15b– d). The exine is semitectate-reticulate, columellate, with short, densely spaced columellae, about 0.8 µm long that diminish in thickness towards the thick foot layer (Text-fig. 15b–e). Lumina are irregular in shape, up to about 1.2 µm in diameter. Muri are about 0.4 µm wide with a rounded profile and are ornamented by minute verrucae aligned in two longitudinal rows that form poorly defined transverse ridges.

A f f i n i t y a n d o t h e r o c c u r r e n c e s. The in situ pollen grains of Asteropollis- type pollen sp. 2 differ from the pollen associated with Hedyflora crystallifera, and also pollen of Asteropollis- type pollen sp. 1 (above), in their smaller size and in having a mainly pentachotomocolpate aperture configuration in contrast to the typical tetrachotomocolpate, or sometimes trichotomocolpate, pollen of Hedyflora crystallifera. Stamens producing the two Asteropollis pollen types (sp. 1 and sp. 2) are also distinct in shape and size. In aperture configuration the pentachotomocolpate grains are more comparable to pollen of Asteropollis asteroides and pollen of extant Hedyosmum (e.g., Walker and Walker 1984).