Flora of North America species comparison

Flowers of Platanthera stricta are evidently mostly scentless or only faintly spicy.

The plants here treated as Platanthera stricta have in common more or less saccate spurs, orbiculate viscidia, and leaves that abruptly diverge from the stem, often at angles approaching 90º (this feature is sometimes obscured in sheltered, deeply shaded habitats). The plants described as P. gracilis Lindley are florally typical of the slender-spurred extreme of P. stricta; they differ only in peculiarly reduced, slenderly oblong but nonetheless abruptly wide-spreading leaves. The plants figured by C. A. Luer (1975) as P. hyperborea var. gracilis (Lindley) Luer are not referable to P. stricta but rather are apparently hybrids of P. stricta and P. dilatata. Critical study of the description of Habenaria borealis var. viridiflora Chamisso and an evident isotype show this plant to be referable to P. stricta, although the name has been applied to P. huronensis in the Northwest and to P. convallariifolia in Japan. See also the discussion under 9. P. convallariifolia.

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

The columns of Platanthera sparsiflora, P. brevifolia, and P. zothecina differ from those of superficially similar species in their comparatively large, diverging, and forward-directed rostellum lobes; they are typical of columns of Platanthera species that deposit pollinaria on insects’ compound eyes. The resulting broad column fills a large portion (generally about 2/3) of the width of the hood formed by the dorsal sepal and petals, and in live and well-prepared herbarium specimens this feature separates these species from their relatives with proportionately smaller, narrower columns. Selection for more generalized pollination mechanisms, as is known elsewhere in the genus, however, has apparently produced derivatives of P. sparsiflora with reduced columns that simulate members of the P. hyperborea complex. The use of column structure, as has been traditionally employed to delimit P. sparsiflora, therefore actually recognizes a pollination syndrome and may not be adequate to represent the evolutionary and systematic status of this group.

Platanthera sparsiflora is highly variable in both vegetative habit and flower structure. Plants may be rather short, stout, with numerous broad leaves scattered along the stem and a rather dense inflorescence of comparatively large flowers. Others are tall and very slender, with few small, ascending leaves widely spaced on the proximal portions of the stem and very lax inflorescences of small flowers (Limnorchis laxiflora Rydberg). Others, with long, usually dense inflorescences of small flowers distal to basal clusters of leaves, have recently been treated as Limnorchis ensifolia by W. A. Weber (1990). These last, also discussed at length by D. S. Correll (1950) under Habenaria sparsiflora var. laxiflora, are characterized by smaller columns in which the reduced rostellum lobes appear to be folded forward, replacing the typical hemispheric chamber with a narrower fissure. Flower size in some plants furthermore may vary greatly in different years. Spurs vary from uniformly tapering to clavate, extending stiffly along the ovary to curving forward, and in length range from slightly shorter than the lip to about 1.6 times its length. In both vegetative and floral characters various degrees of intermediacy and combinations of character extremes occur. The complex including the three species recognized here is currently under critical study.

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