Platanthera nivea
Platanthera orbiculata
snowy orchid
large round-leaf orchid, large round-leaf rein orchid, lesser roundleaf orchid, round-leaf bog-orchid, round-leaf orchid
1–3, ascending to spreading, abruptly or gradually reduced to bracts distally, often fugaceous and withered at anthesis;
blade linear to linear-lanceolate, 3–31 × 0.3–2 cm.
2, in subequal basal pair lying on ground;
bracts (very rarely, 0–)1–6, scattered along stem;
blade broadly elliptic to orbiculate or oblate, 5–21 × 3–22 cm.
dense.
lax to dense.
not resupinate, showy, white;
lateral sepals spreading;
petals linear-oblong to oblong or elliptic, falcate, basally somewhat dilated, margins entire;
lip reflexed ± at middle, linear-elliptic to linear-oblong, without basal thickening, 3–8 × 1–3 mm, margins entire;
spur slenderly cylindric, 10–18 mm;
rostellum lobes directed downward, very short, obscure, rounded;
pollinaria straight, pollinia remaining enclosed in anther sacs;
viscidia oblong to linear-oblong;
ovary slender, 4–12 mm.
resupinate, rather showy;
calyx mostly greenish white;
corolla mostly white;
lateral sepals reflexed to somewhat spreading;
petals lanceolate-falcate, margins entire;
lip descending to somewhat reflexed, linear-oblong to linear-lanceolate, without basal thickening, 7–17 × 1–2.5 mm, margins entire;
spur slenderly clavate, 14–27 mm;
rostellum lobes directed strongly forward, wide-spreading, angular;
pollinaria nearly straight, 3–4.5(–4.8, very rarely) mm;
pollinia remaining enclosed in anther sacs;
viscidia orbiculate;
ovary slender to rather stout, mostly 10–26 mm.
= 42.
Platanthera nivea
Platanthera orbiculata
The column of Platanthera nivea is similar to that of P. clavellata and P. integra and unlike that of other Platanthera species. The columns of these three species bear two pairs of appendages. In P. nivea, on either side of the column and flanking the anther sacs, a cushionlike flap simulates a pollinium; below these structures, elongated slender processes parallel the basal margins of the lip, similar to the situation in Habenaria. Together with its non-resupinate flower and perhaps elongate-spheroidal tuberoids, these characteristics suggest that this species should not be included in Platanthera.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
The key will permit determination of most specimens of Platanthera orbiculata and P. macrophylla. More precise discrimination of ambiguous specimens is possible by use of the formula from A. H. Reddoch and J. M. Reddoch (1993): spur length + (2 × pollinarium length), which for P. orbiculata is less than 38 and for P. macrophylla is equal to or greater than 38.
Considerable variation in size and shape of leaves occurs, and although to some extent regional in nature, intergradation is complete; recognition of infraspecific taxa is unwarranted. A few collections from isolated areas on the Pacific Coast of Canada are noteworthy, however. Those are small, few-flowered plants with rather narrow leaves borne alternately or suboppositely toward the base of the stem, as in some Asiatic species. They are in some respects very similar to Platanthera freynii Kränzlin, an Asiatic species distinguished primarily by its abruptly narrowed petals, in contrast to the generally broader, but variable, petals in North American plants. These western plants warrant further study to establish their identity and to elucidate relationships between North American and Asiatic species.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
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