Petalochilus

Little more is known of this genus than was recorded by Rogers in the original descriptions and illustrations. There is no point then in repeating his observations, especially since his paper has been reprinted in Transactions and so is readily available to local students.

Text Figure 1.

Petalochilus is considered to be a local development, probably derived from an early form of Caladenia carnea. The undifferentiated labellum is not of itself important. The specialised labellum of the average orchid is a petal adapted to the requirements of pollination. When that function is taken over by another organ (as happens in Petalochilus) the labellum falls into disuse and thence into decline, reverting in this instance to its original petaloid condition. Petalochilus then appears to be a retrograde to Caladenia rather than the representative of a primitive form. Nicholls (Vict. Natr., 61, 1945, 207; figs. k, 1, m) has unconsciously demonstrated that Caladenia could give rise to such a form as Petalochilus. He describes a couple of teratological specimens of Caladenia menziesii R. Br. in which the labellum has become petaloid, although still retaining vestigal calli,

and the column-wings have fused to form a cavity embracing the lower two-thirds of the column. The staminoid appendage. which distinguishes Petalochilus is, however, absent in these Caladenia specimens.

Petalochilus saccatus is probably derived from an early form of P. calyciformis by a fusion of the column-wings with the staminoid appendage.