Subtribe Spiranthinae - The Pollination Biology of North American Orchids: North of Florida and Mexico - page 27

Table 2.3 Pollinators of Spiranthes casei and S. cernua
Species Pollinator/state or province References

S. casei Apidae

Bombus terricola Kirby/NY Sheviak ( 1982 )

Halictidae
Dialictus versans (Lov.)/ON

Catling ( 1980b, 1983c )

S. cernua Apidae

B. fervidus (Fabricios)/NH

Sheviak ( 1982 )

NY Sheviak ( 1982 )

VT Sheviak ( 1982 )

NS Catling ( 1980b, 1983c )

NH Luer ( 1975 ), p. 120

B. impatiens Cresson/MA Sheviak ( 1982 )

B. terricola Kirby/NY, KS Sheviak ( 1982 )

B. sp./NY, NE Sheviak ( 1982 )

NC Stevenson ( 1973 )

Halictidae
D. sp./NC

Stevenson ( 1973 )

confirmed earlier reports (Leavitt 1900, 1901 ; Swamy 1948 ) that agamospermy in
the S. cernua complex occurs by adventitious embryony. While the flower is still in
bud and at about the time the megasporocyte undergoes its first division, one or two
cell layers of the inner integument, usually in an area near the micropylar end of the
ovule, start to enlarge and divide (Swamy 1948 ; Catling 1982 ). By anthesis or sev-
eral days thereafter, proliferation in this area has produced 10-30 sometimes greatly
enlarged cells, and degeneration of the nucellus has occurred (Catling 1982 ).
Embryo sac development usually fails to proceed beyond the 4-nucleate stage
(Swamy 1948 ; Catling 1980b, 1982 ; Lakshmanan and Ambegaokar 1984 ). The
enlarged cells ultimately give rise to one or multiple embryos.
Unlike Leavitt ( 1900 ), Swamy ( 1948 ) found that in a few collections of “ S. cer-
nua ” individual capsules sometimes contained both seeds with adventitious embryos
and seeds with embryos derived from the fertilization of normally developed embryo
sacs. Although in asexual individuals adventive embryos developed very early, in
these so-called “intermediate” individuals their development was delayed until after
the normally developed ovules had been fertilized.
The northeastern species of Spiranthes studied by Catling ( 1980b, 1982 ) differ
from many plants with adventitious embryony in not needing pollination to stimu-
late development of the embryo (pseudogamy), but this does not mean that aga-
mospermy is obligate (Leavitt 1901 ; Stebbins 1941 ; Maheshwari 1952 ; Catling
1982 ). None of the taxa with adventitious embryony have lost the morphological
features required for pollination (Catling 1981, 1982 ; Sheviak 1982 ). The flowers
remain in anthesis 3-10 days, secrete nectar, are functionally capable of pollen pro-
duction and reception, may emit a characteristic fragrance (Catling 1980b, 1982 ),
and are frequently pollinated by insects (Tables 2.3 - 2.9 ).