Tribe Calypsoeae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 123

Floral Morphology
The flowers are resupinate and vary in size and number (Table 6.4 ). They can be
inconspicuous or showy and loosely to densely arranged in short to long racemose
inflorescences (Freudenstein 1997, 1999 ; Magrath and Freudenstein 2002 ).
C. odontorhiza produces both chasmogamous and cleistogamous flowers (Fig. 6.5 ).
These occur on separate plants, sometimes in a single population, with cleistoga-
mous individuals more common over the range of the species (Magrath and
Freudenstein 2002 ). The flowers of C. bentleyi are also cleistogamous with red lips
at some sites and chasmogamous with yellow lips at others (Fig. 6.6 ) (Freudenstein
1999 ; Horwitz 2006 ).
The sepals and lateral petals may be spreading, curved, or directed forward, with
the petals almost clasping the column in C. trifida (Fig. 6.7a ) (Freudenstein 1997 ).
In C. odontorhiza , C. trifida , and C. maculata the lateral sepals unite with the base
of the labellum and column at the top of the ovary forming a mentum or small spur,
more prominent in the latter than in the other two species (Fig. 6.8b ) (Freudenstein
1997 ). The dorsal sepal, spreading to sometimes arching over the column, is con-
nivent with the lateral petals in chasmogamous members of C. odontorhiza to form
a hood over the flowers (Fig. 6.5a, b ).
The labellum varies in shape and may be lobed or unlobed (Figs. 6.5a, b , 6.6b ,
6.7a , 6.8a , and 6.9a, b ) (Freudenstein 1997, 1999 ). It is narrowed basally to a short
claw, 0.4-1.0 mm wide. Basal lamellae or ridges are present and vary from 1.5 to
4 mm in length. In C. bentleyi and C. striata , they are thickened and fused into a
callus, and the labellar margins are involute (Figs. 6.6b and 6.9a ).
The column varies in size (Table 6.4 ) and is straight to strongly curved toward
the labellum It bears two pairs of hard, superposed, unequal pollinia at its apex in a
fully encumbent, operculate anther (Figs. 6.5 - 6.9 ) (Freudenstein 1997 ). The pollinia
have a common stalk as part of a single pollinarium. The stalk comprises a stipe
with an adhesive base and a distal end that connects to the pollinia via elastic cau-
dicles, visible as soon as the anther opens (Claessens and Kleynen 1998 ). The stipe
in many members of the Calypsoeae, including Aplectrum and Corallorhiza , is
termed a hamulus (Freudenstein 1994a ). It is derived from an upwardly curved
extension of the rostellar apex that attaches to the caudicles (Freudenstein 1994a, b ).
Because of its placement at the apex of the rostellum, rotation at its base can effect
a transfer of the pollinia from their usual position on the dorsal side of the rostellum
to the ventral side, where the stigma is located (e.g., Fig. 6.8e, f ) (Freudenstein
1994a, 1997 ). The hamulus remains attached to the pollinia following contact with
the stigma, permitting identification of those flowers that have self-pollinated
(Catling 1983 ). It and other components of the rostellum are very reduced or absent
in cleistogamous plants of C. odontorhiza and are poorly developed in C. trifida and
Aplectrum (compare Fig. 6.5c , d and 6.5e, f ) . In addition, a pair of adaxial auricles
at the base of the column, which guides the pollinator's proboscis, is much less well
developed in cleistogamous plants. The stigmatic surface is concave, viscid, and
variously shaped, usually with an orientation perpendicular to the long axis of the
column (Table 6.4 ).