About Caladenia rigida R.S.Rogers
Caladenia rigida is a terrestrial, perennial, deciduous herb. It grows from an underground tuber and produces a single hairy leaf, 80–200 mm (3–8 in) long and 8–10 mm (0.3–0.4 in) wide. One or two white flowers marked with fine reddish-brown lines, each 40–60 mm (1.6–2.4 in) across, are borne on a 150–300 mm (6–10 in) tall flowering spike. Only the sepals, not the petals, have red, reddish-black, or yellow-green glandular tips that measure 8–12 mm (0.3–0.5 in) long. The dorsal sepal is erect near its base, then curves gently forward; it is 25–45 mm (1–2 in) long and approximately 3 mm (0.1 in) wide. The lateral sepals are 40–50 mm (1.6–2.0 in) long and 4–7 mm (0.2–0.3 in) wide, and spread stiffly apart from each other. The petals are 25–37 mm (0.98–1.5 in) long and 3–5 mm (0.1–0.2 in) wide, and are arranged in a similar way to the lateral sepals. The labellum is 14–16 mm (0.55–0.63 in) long, 9–11 mm (0.35–0.43 in) wide, and is white in colour. The sides of the labellum have many red, linear teeth up to 1.5 mm (0.06 in) long with white tips, and the tip of the labellum curves downwards. Four or six rows of red calli with white tips run along the mid-line of the labellum. Flowering occurs from August to October. This species, commonly called the stiff spider orchid, is only known from the Mount Lofty Ranges, where it grows on the upper slopes of hills in open forest with an open shrub layer. Ecologically, this orchid appears to attract pollinators through two methods: sexual deception of thynnid wasps, and offering food rewards to other insect species. The species does not need fire to flower, but some populations seem to benefit from fire, possibly because fire reduces competition from other species, including grasses.
