Caladenia orchids in flower

Spider-orchids and White Fingers

Shows pair White Fingers, Edward Hunter Heritage Bush Reserve

White Fingers, Caladenia catenata

A range of Spider-orchids and White Fingers (C. catenatus) have been flowering, lately.

Caladenia orchids including White fingers (P. catenatus) and Tiny fingers (P. pusilla) as well as the Southern spider-orchid (C. australis), Green-comb spider-orchid (C. dilata), Candy spider-orchid (C. versicolor), and the Crimson and Scented Spider-orchids have been recorded in the Reserve in the Atlas of Australia and a list developed in 1989 by AJ Rayner, a resident of Moe. The Wine-lipped spider-orchid (C. oenochila) has also been seen.

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Some of the spider-orchids are from the reticulata group with petals/ sepal ends clubbed with dense osmophores (which produce scent) and some are from the pattersonii group where the tips are filament-like with a dusting of osmophores on the ends.

Where they grow

Most Caladenia occur in heath, heathy, shrubby and grassy woodlands, and drier open forests (Backhouse, 2011). They can be found flowering here from September of each year accompanied by parrot-peas and bush-peas.

Shows woodland area with flowering parrot-pea and bush-pea, Edward Hunter Heritage Bush Reserve

Flowering pea in September

Shows pea flowers in Edward Hunter Heritage Bush Reserve

The flowering of peas is quite dense this year

How they grow

They grow actively in the winter, started by the drop in temperature and an increase in soil moisture with autumn rains (Backhouse, 2011). A shoot then develops from the previous season’s underground tuber, and a single hairy leaf is produced. A structure called the dropper is sent to depth in the soil where it stores starch, nutrients and water ready for summer dormancy.

The flower grows from the base of the leaf once the leaf has fully expanded. Some of these orchids use sexual deception to lure male thynnid wasps into attempting to mate, thereby transferring the pollinia to the next flower. Others use food deception, using scent to attract insects such as native bees. Once pollination occurs, the ovary matures within four to six weeks and around 30,000 seeds are produced when the seed capsule splits. These – of which an estimated 1% strike – disperse into dry soil (Dixon & Tremblay, 2009).

These seeds start to grow when there is enough moisture, suitable temperatures (15 to 20°C) and a specific type of fungus to support the growth of the plant. It is not known how long it takes for a flower to form from seed but laboratory tests indicate a three year interval. Mycorrhizae – fungi symbioses – are critical to germination and storage. The soil seed bank remains viable only for a while – estimated at around four months (Dixon & Tremblay, 2009).

References

Backhouse, G. (2011). Spider-Orchids: The Genus Caladenia and its Relatives in Australia. Gary Backhouse: Melbourne. [CD].

Dixon, K. & Tremblay, R.L. (2009) Biology and natural history of Caladenia. Australian Journal of Botany, 57, 247–258.

Rowan, C. & Rowan, M. (2014) Native Orchids of Australia, http://www.retiredaussies.com/ [website]

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