Early Morning anthesis

Flowers of Thysanotus chinensis (Liliaceae) open fully between around 7 am and 9 am. It was listed as rare in previous biodiversity survey.

Early morning anthesis is a common phenomenon scattered through angiosperms. Flowers of the early morning anthesis species open in early morning, probably soon after dawn and close before or around mid-day. It is suggested to prevent heat stress as anther and stigma would be destroyed by over-heating and closure of flowers would also reduce transpiration. These are reasonable explainations as most of the early morning anthesis species are herbaceous, grassland inhabitants.

It is important to note that early morning anthesis should be more related to the pollinator activity where it is the ultimate goal of floral anthesis. After a quick search on the literatures, bees were reported to be the major pollinators of early morning anthesis species including Pyrrhopappus carolinianus (Asteraceae) (Estes and Thorp, 1975) and Cassia fasciculata (Caesalpiniaceae) (Thorp and Estes, 1975). Bees were reported to forage actively for the pollen after dawn and their activities quickly reduced towards the mid-day. The close relationship between pollinator activity and timing of anthesis is interesting and I think the early morning thesis species in Hong Kong are also pollinated by bees as certain groups of them are particularly active in the morning. There is a number of candidates for observation including the ones shown here, namely Geissapis cristata (Fabaceae), Thysanotus chinensis (Liliaceae) and Xyris pauciflora (Xyridaceae).

Geissapis cristata (Fabaceae) is another rare species in Hong Kong which inhabits lowland wetland.

Xyris pauciflora (Xyridaceae) is commonly found near wet places in Hong Kong. All of the species listed here are having brightly-colored corolla. It is an important feature to send visual signal to pollinators and to offer them a landing place.

References:

Estes J.R. and Thorp R.W. (1975) Pollination Ecology of Pyrrhopappus carolinianus (Compositae). American Journal of Botany 62: 148-159.

Thorp R.W. and Estes J.R. (1975) Intrafloral behavior of bees on flowers of Cassia fasciculata. Journal of the Kansas Entomological Society 48: 175-184.