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Hexalectris Rafinesque
Kennedy and Watson ( 2010 ) recently revised the genus Hexalectris and proposed
several significant changes in nomenclature and distribution. However, pending fur-
ther study, the present discussion follows the treatments of Goldman et al. ( 2002 )
and Catling ( 2004 ).
Hexalectris is a mostly Mexican genus of seven mycoheterotrophic species often
confused with Corallorhiza , but differing, among other things, in having a number
of raised crests running down the center of the lip (Fig. 7.2b ) (Coleman 2002 ). Two
species are found only in Mexico or Mexico and Guatemala, but five others extend
into the USA. All, except the widespread H. spicata (Walter) Barnhart var. spicata
(crested coralroot), are restricted to scattered sites in Texas, New Mexico, and
!RIZONA'OLDMANETAL 2002 ). Limited information on pollination biology is avail-
able for H. nitida L. O. Williams (Shining or Chisos or Glass Mountain coralroot),
H. spicata (Walter) Barnhart variety arizonica (S. Watson) Catling and V. S. Engel
!RIZONACRESTEDCORALROOT H. revoluta Correll variety revoluta (Curly corralroot,
Correll's cock's-comb), and variety colemanii Catling (Coleman's coralroot).
H. nitida includes forms having open flowers with revolute sepals and petals
(Luer 1975 ) and others with predominantly closed flowers (Engel 1987 ). Catling
( 1990, 2004 ) reported autogamy for this species: the holotype has no rostellum, and
the pollinia develop in direct contact with the stigmatic surface.
H. spicata var. arizonica is also autogamous, routinely lacks a rostellum, and
usually has a connivent or only a slightly spreading perianth (Catling 1990, 2004 :
Catling and Engel 1993 ). Open flowers (Fig. 7.2b ) have only been reported in a
single, predominantly cleistogamous population near Dallas. The tips of the anthers
in open flowers are dehydrated, pointed, and reddish, whereas in closed flowers they
are enlarged, green, and fleshy. The distended anther tips in closed flowers along
WITHATERMINALLYEXPANDEDMIDVEINONTHELIPMAYCONTRIBUTETOSQUEEZINGTHE
pollinia onto the stigmatic surface as the column stretches and buckles during the
aging process (Catling and Engel 1993 ). Coleman ( 2002 ), however, reported that
the pollinia slide from under the anther cap early on and are present on the stigma
in freshly opened and in young cleistogamous flowers.
Autogamy also occurs in H. revoluta Correll var. revoluta (Catling 2004 ). In this
case, the evidence suggests that the pollen masses rotate onto the stigmatic surface
following elevation of the anther cap. Catling ( 2004 ) observed a pollinarium with
the viscidium still attached to the edge of the rostellum but with four pollinia resting
on the stigmatic surface and firmly attached there by developing pollen tubes. The
second variety, H. revoluta var. colemanii , is an obligately outbreeding taxon with a
distinct rostellum (Catling 2004 ).
Insects may also cross-pollinate the flowers of H. revoluta var. revoluta and open
flowers of H. nitida or H. spicata var. arizonica , but this has yet to be demonstrated
(Catling and Engel 1993 2ECENTOBSERVATIONSIN H. nitida suggest that autogamy
here might be obligate (Catling 2004 %VENIFOUTCROSSINGOCCURSHYBRIDIZATION
between the varieties of H. spicata would likely be restricted by differences in
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