Flower size variation in Danhatchia (Orchidaceae)

Danhatchia novaehollandiae D.L.Jones & M.A.Clem. and D. australis (Hatch) Garay & Christenson were separated at species rank due to differences in petal length and flower opening, with the Australian species having smaller, tardily opening flowers. From this, flower lengths for Australia and New Zealand are expected to be bi-modally distributed with peaks at c. 3 mm and c. 5 mm respectively. Flowers on all available herbarium specimens in AK, CANB, and NSW were measured, and flower length was found to be unimodal, with nearly identical ranges in Australian and New Zealand plants. Flower size variation in Australian and New Zealand Danhatchia specimens has two significant contributing components, inter-individual variation, and ontogenetic variation where flowers increase in size as they age. Dimensions previously recorded for the two species reflect upper and lower limits on the range of variation in flower size present in both New Zealand and Australia, respectively. Within herbarium material, 20% of flowers on New Zealand specimens, and 40% of flowers on Australian specimens exhibited signs of opening. There was no correlation between flower size and opening, as might be expected if the two species were both present in Australia and/or New Zealand. Neither the biogeographic context, pollination system, nor morphological evidence support Danhatchia australis and D. novaehollandiae as distinct species.