Flora of North America species comparison

The rostellum lobes in Platanthera cristata normally are only slightly curved, presenting the viscidia in a generally forward position. Considerable variation is apparent, however, and sometimes a marked curvature similar to that in P. chapmanii is seen, apparently presenting the viscidia downward. These orientations are difficult to assess in distorted herbarium material, and the species is in need of further study. The triangular mouth of the spur of P. cristata is distinctive, however, and can aid in determination of confusing material (see also below and the discussion under 29. P. chapmanii).

Platanthera pallida P. M. Brown was recently proposed to accommodate two populations of pale-flowered plants on Long Island, New York. Their distinctive nature has long been apparent. In the field, pollination normally is rapid and the flowers senesce while small and yellowish, but in cultivation in the absence of pollinators, flowers remain open for an extended period during which the lips elongate markedly and the flowers fade to a dull white. Hence they suggest P. ×canbyi (Ames) Luer [P. blephariglottis × P. cristata], but they differ in their much shorter spurs.

Plants of Platanthera pallida were reported to differ from P. cristata in shorter spurs, entire dorsal sepals, and lateral sepal and lip orientation. The range of spur lengths in P. cristata, however, is much greater than specified and in fact includes the range of P. pallida. Dorsal sepals with entire margins are commonly seen also in P. cristata, and those of P. pallida may be deeply emarginate. Lateral sepal and lip orientation tend to differ in the two taxa, but the conditions typical of each taxon can be found in the other. The keyhole shaped orifice of the spur in P. pallida mentioned by Brown is a unique feature, but it is present in only a small percentage of individuals and completely intergrades to the triangular orifice of P. cristata. Furthermore, superficially similar pale-flowered plants from farther west on Long Island are more similar to typical P. cristata and hence possibly indicative of a cline. The plants described as P. pallida therefore appear to represent neither a distinct species nor are they merely hybrids; they seem to be partially stabilized introgression products and potentially useful subjects for evolutionary study.

Hybrids of Platanthera cristata with P. blephariglottis are P. ×canbyi (Ames) Luer and with P. ciliaris are P. ×channellii Folsom; until recently the latter was confused with P. chapmanii.

(Discussion copyrighted by Flora of North America; reprinted with permission.)

Of conservation concern.

Only recently described, the original publication separated Platanthera zothecina from P. sparsiflora solely on the basis of the former’s spur/lip length ratio of 1.5 and few-flowered habit. In fact, the range in ratios overlaps, with a range of at least 1.3–2.6 in P. zothecina and 0.7–1.6 in P. sparsiflora. Actual spur lengths are more useful for determination, and perhaps more significant, because they may indicate specialization for different pollinators; the very limited overlap in spur lengths supports recognition of P. zothecina. Other features support the separation. The thickened median ridge toward the base of the lip characteristic of P. sparsiflora seems to be lacking in P. zothecina, which instead seems to display a parallel series of low ridges, but this distinction unfortunately cannot be established with certainty from the limited sample available. The columns should be investigated in detail, for a limited sample suggests differences in orientation of anther sacs and rostellum lobes. Platanthera sparsiflora is often fewer flowered than P. zothecina, but the typically few-flowered inflorescences of the latter distal to the broad, spreading, and commonly succulent leaves of an often peculiar whitish green color, contribute a markedly distinctive appearance to the plant.

Because of the restricted distribution of Platanthera zothecina and its recent description, the species is poorly known; the description here is based on few specimens and hence apt to be too restrictive.

(Discussion copyrighted by Flora of North America; reprinted with permission.)