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.)

Platanthera convallariifolia is commonly reported from the Aleutians and adjacent coastal Alaska based on short, very broad-leaved plants with rather large flowers in dense, thick inflorescences. Those plants, however, apparently represent robust, maritime phenotypes of P. huronensis or in some cases P. stricta or P. dilatata comparable to those seen in Piperia elegans and Spiranthes romanzoffiana. In fact, typical Asiatic Platanthera convallariifolia is a slender-leaved plant entirely comparable in habit to P. huronensis. The two species are very similar, and they share a tetraploid chromosome number. Typical Asiatic P. convallariifolia is characterized by a linear lip and clavate spur about 2/3 to nearly the length of the lip. The lip occasionally varies to slightly lanceolate and the spur to somewhat saccate. The column appears somewhat broader than in P. huronensis, and viscidia also are apparently rather broad. A few specimens from the Aleutians and Alaskan peninsula exhibit these floral characteristics. Vegetatively, however, some Alaskan material is distinctive in the position and orientation of the leaves. In floral and vegetative characters, Alaskan plants furthermore intergrade with P. huronensis. Whether Alaskan plants are truly referable to P. convallariifolia is uncertain, and the status of the Asiatic species also needs study. Both P. convallariifolia and the Alaskan plants here referred to it appear to combine features of P. huronensis and P. stricta. Platanthera convallariifolia may have arisen through hybridization of these two species, or of P. stricta and P. dilatata, thus accounting for the difficulty in identification. The description presented here is based on few Alaskan plants and is apt to be too restrictive; therefore the poor understanding of the plant makes the present delimitation and distinctions from P. huronensis rather arbitrary.

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