Thursday, April 7, 2011

Carex canina

Carex canina (Cyperaceae) is a highly restricted species which is only found in a few places in Guangdong, China including Hong Kong. It is therefore an endemic to Guangdong province. Nevertheless, it is not common at all in these localities where in the case of Hong Kong, Sunset Peak is the only locality where C. canina could be found.
Achenes of Carex canina are trigonous just like most other Carex species. It looks a bit special than the others as the angles and faces of the achenes are conspicuously contricted forming a ring of constriction at the middle part of it (as shown in the photograph above). Its achenes also have a long beak at the apex which is about 1 mm long. By combining these features, this makes C. canina quite unique among the numerous Carex species recorded in Hong Kong.

Seed dispersal of Carex species is not well documented particulary in the old world. Seeds are not brightly coloured and without fleshy part for attracting mammals and birds. Seeds are not light enough nor winged for wind-dispersal. Studies from the America suggested that many of them are dispersed by ants (Handel, 1976; Vellend et al., 2000). High endemism of Carex species, especially for the forest-understorey species, does support this hypothesis as dispersal by ants is not as effective as vertebrate-dispersal although herbaceous species are always having higher endemism than the woody species (Hamrick et al., 1992; Shaw, 1999).

Hamrick J., M. J. W. Godt and S. L. Sherman-Broyles (1992) Factors influencing levels of genetic diversity in woody plant species. New Forests 6:95-124.
Handel S. N. (1976) Dispersal ecology of Carex pedunculata (Cyperaceae), a new North American myrmecochore. American Journal of Botany 63: 1071-1079.
Shaw J. C. (1999) The conservation status of Cyperaceae in Hong Kong. Porcupine 19: 16-18.
Vellend M., M. J. Lechowicz and M. J. Waterway (2000) Germination and establishment of forest sedges (Carex, Cyperaceae): tests for home-site advantage and effects of leaf litter. American Journal of Botany 87: 1517-1525.

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