Inside a Bunny Orchid

Greetings fellow foxies,
Bunny orchids Eriochilus species are endemic to Australia, with six of the eight species occurring in the south-west of Western Australia. In Foxes Lair  the common bunny orchid Eriochilus multiflorus subsp. multiflorus and crinkle-leaf bunny orchid Eriochilus multiflorus subsp. undulatus are flowering now. The common bunny orchid has more flowers per head, prefers gravel soils, and and begins flowering about a week earlier than crinkle-leaf. Flowers have a delightful structure.

​Caladenia genus (of spider orchid fame) is the closest relative, but there are marked differences.

• Eriochilus species flower from April to June, much earier than most Caladenias
• Flowers are quite 'woolly' (particularly the labellum), mostly white with smooth leaves and stem.
• They are one of the few orchids which produce nectar to attract their native bee pollinator. The local species pollinator is a tiny masked bee Hylaeus dorothiae.

Hylaeus sp. image Melanie Cooper

After taking many closeup images to see if I could find any difference in flower structure (no), I was mystified by the anther placement. Anthers are covered by a two-part cover (anther hood), which sits almost directly on top of the cave-like stigma. I couldn't figure out how a bee entering the stigma could come into contact with pollen. Examination of flowers at all stages  of maturity showed no difference in the closed anther hood, although I did find pollen inside a finishing flower. Luckily I found  a broken stem with  wilted flowers and brought the sample back for dissection.

Aha, The dissection revealed a pollinium under the anther hood. Here the single anther produces sacs of pollen connected by a filament to a sticky disc called a viscidium. The viscidum dangles out of the anther hood and sticks on a bee that touches it. The bee flies away with the dangling pollen sac and carries it into the next flower's stigma. in the last image below, pollen sacs have been deposited next to the dying flower's stigma. One has burst to release pollen.

Two viscidia poking out from anther hood

Anther hood cut vertically to show pollinium

pollen sacs left next to stigma of finishing flower