Watsonia humilis Mill. is endemic to the Western Cape area of South Africa. It is winter growing and summer dormant like many other South African irids, restricted to a particular fynbos association on seasonally wet clay and loamy alluvial flats.
Its original range in the Breede River Valley between Tulbagh and Worcester, and the lowlands between Malmesbury, Franschhoek and Gordon’s Bay, has been reduced by 98%. Two populations are known to remain: one of fewer than 50 plants in an urban reserve at Gordon’s Bay and a second rediscovered in 2012 in the Breede River Valley near Wolseley, more than 80 km away. A third population may still exist between Somerset West and Sir Lowry’s Pass despite bulldozing by vandals in 2011.
Although critically rare in its natural habitat, it is secure in ex situ cultivation around the world. At least one strain has been passed between gardeners in Australia since its first importation in the 1830s.
Watsonia humilis is in the section Watsonia, subsection Watsonia of the genus. It is distinguished by its small size, unbranched inflorescence, strongly keeled bracts with outcurved tips and stamen filaments no longer than the perianth tube. Its pale coloured perianth (pale pink to white, never red) suggests that it is adapted to insect pollination unlike its larger and usually red-flowered relatives.
This watsonia can be grown in the open garden here but to keep track of the corms I grow it in 20 cm pots, lifting and dividing each summer. It multiplies vegetatively and I have used it as the ovule parent in hybridization.
The common form in Australian gardens has white perianth lobes and a tube shading to deep pink at the base. The F1 hybrids with bright red flowered W. meriana Mill. have uniformly pale pink flowers, the intensity and hue of the pink (anthocyanin) pigmentation varying slightly between individuals. This result shows that white flowers in this species have a different genetic basis to the recessive acyanic mutants of other species: it suggests incomplete dominance, possibly with more than one genetic locus involved. This is to be expected if white flowers were a stabilised local adaptation in the source population, rather than a passing mutation as in W. borbonica ‘Arderne’s White’. These hybrids lack the outcurved bract tips of W. humilis, which may be the most useful diagnostic character for recognising it.
Goldblatt, P. (1989) The genus Watsonia. (National Botanic Gardens: Kirstenbosch) ISBN 062012517
Goldblatt, P., Manning, J.C., Raimondo, D. & von Staden, L. (2013) Watsonia humilis Mill. National Assessment: Red List of South African Plants version 2013.1. Accessed on 2014/1/28.