Biology Reference
In-Depth Information
Although, according to Goldman et al. (
2004
),
C. barbatus
is the only
Calopogon
that completely lacks floral fragrance, the flowers of
C. tuberosus
are also often
described as odorless or faintly scented; they produce no nectar and the pollen is not
usually collected for food (Stoutamire
1971
; Thien and Marcks
1972
; Dressler
1993
; Goldman et al.
2002b
). The flowers of
Pogonia
emit a mild, sweet odor and
may produce very small amounts of nectar in a small tube-like nectary formed by
the convergence of the column and lip (Guignard
1879
; Heinrich
1975
; Gregg
1991
). According to Thien and Marcks (
1972
),
Arethusa
also produces a floral odor
and a very small amount of nectar. Yannetti (
1996
) reported the presence of fra-
grance in 15-20% of the plants at a site in the Pine Barrens of southern New Jersey
and described a well-developed nectary, lined with papillose cells, concealed within
the ovary. He speculated that the direction of evolution proceeded from a system of
reward to one of deceit, but that some fragrant plants retained the capacity to pro-
duce a little nectar. Stoutamire (
1971
) was neither able to detect any odor nor find
any liquid in the flower and concluded that nectar was either absent or the pollina-
tors obtained it by piercing the tissues. Dressler (
1993
) also characterized the
Arethusinae as nectarless.
Compatibility and Breeding System
The flowers of
C. tuberosus
, once thought to be capable only of outcrossing (e.g.,
Thien and Marcks
1972
), are now known to be self-compatible (Table
8.2
). In a
study in northern Florida, Thien (
1973
) found that 67% of artificially self-pollinated
flowers produced fruit. Similarly, Firmage and Cole (
1988
) reported that 87% of
artificially self-pollinated flowers and 61% of geitonogamous pollinations in south
central Maine produced fruit compared to 83% of cross-pollinated plants. However,
insects are required for pollination: no fruit was set in enclosed, unmanipulated
plants (Firmage and Cole
1988
5NDERNATURALCONDITIONSTHEPOLLINATIONMECHA-
nism (see below) probably reduces selfing in individual flowers while the timing of
flower opening reduces transfer of pollen among flowers on a single plant (Thien
and Marcks
1972
; Thien
1973
; Firmage and Cole
1988
).
Pogonia
and
Arethusa
are similarly self-compatible (Table
8.2
). Artificial self-
pollination produced fruit sets of 89-95% in
P. ophioglossoides
and about 95% in
A. bulbosa
(Thien and Marcks
1972
; Thien
1973
). However, flower structure and
number indicate both are also adapted to outcrossing (see below) (Robertson
1887
;
Guignard
1879
; Thien and Marcks
1972
).
Evaluations of intergeneric crosses in the three orchids, based on the develop-
ment of F1 seeds with embryos, indicate that
A. bulbosa
and
C. tuberosus
are inter-
fertile (Thien and Marcks
1972
), and a naturally occurring hybrid has been reported
in Newfoundland (Pinkepank
1993
). Plastid DNA sequences support a close rela-
tionship between
Calopogon
and
Arethusa
(Goldman
2000
; Goldman et al.
2001
).
Crosses of either of these species with
Pogonia
are usually sterile; occasional high
seed production with
Pogonia
as the female parent is attributed to apomixis (Thien
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