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Cleistogamy in Griffithella hookeriana (Podostemaceae)
Abstract
Floral phenology, flower morphology and pollination biology were studied in
Griffithella hookeriana, an endemic and poorly known species. Here we show
that pollination is typically cleistogamous and the species is an obligate
inbreeder. The flowers lack petals and sepals. The essential organs are covered
by a spathe, surrounded by 2 or 3 pairs of bracts. The two anthers that are
borne on a forked filament are placed adjacent to the globular ovary. A pair
of staminodes arise from the base of the anther filament. The style is absent
and the ovary bears two spoon-shaped stigmatic lobes at the apex. Pollination
occurs before anthesis. This is affected by close proximity of the stigmatic
lobes and the anthers and en masse transference of pollen grains (that occur
in pairs, dyads) to the stigma. A large number of pollen grains germinate on
the stigma and the pollen tubes enter the ovules 16–18h after pollination.
Fruits are anisolobous, stalked and rounded and dehisce by means of an oblique
slit. The average number of seeds per fruit is 115 ± 43.4. Flower to
fruit ratio is close to 1:1 and the ovule to seed ratio is 3:1.
South African
Journal of Botany 2001, 67 (2): 320–324
Griffithella hookeriana, an endemic and poorly known species. Here we show
that pollination is typically cleistogamous and the species is an obligate
inbreeder. The flowers lack petals and sepals. The essential organs are covered
by a spathe, surrounded by 2 or 3 pairs of bracts. The two anthers that are
borne on a forked filament are placed adjacent to the globular ovary. A pair
of staminodes arise from the base of the anther filament. The style is absent
and the ovary bears two spoon-shaped stigmatic lobes at the apex. Pollination
occurs before anthesis. This is affected by close proximity of the stigmatic
lobes and the anthers and en masse transference of pollen grains (that occur
in pairs, dyads) to the stigma. A large number of pollen grains germinate on
the stigma and the pollen tubes enter the ovules 16–18h after pollination.
Fruits are anisolobous, stalked and rounded and dehisce by means of an oblique
slit. The average number of seeds per fruit is 115 ± 43.4. Flower to
fruit ratio is close to 1:1 and the ovule to seed ratio is 3:1.
South African
Journal of Botany 2001, 67 (2): 320–324
