Platanthera orbiculata
Platanthera limosa
large round-leaf orchid, large round-leaf rein orchid, lesser roundleaf orchid, round-leaf bog-orchid, round-leaf orchid
Thurber's bog orchid
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.
few to several, spreading-ascending on base of stem, gradually reduced to bracts upwards;
blade lanceolate, 9–28 × 1.2–3.5 cm.
lax to dense.
dense to lax.
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.
resupinate, inconspicuous, green;
lateral sepals reflexed to spreading;
petals lanceolate-, ovate-oblong-, or ovate-falcate, margins entire;
lip descending to reflexed, linear-oblong, linear-elliptic, or rhombic-ovate, usually with inconspicuous to scarcely discernable (possibly sometimes absent) median basal thickening, 2.5–8.5 × less than 1–3.5 mm, margins entire;
spur filiform, tapering toward apex, very rarely filiform-conic from slightly stout base, 8–25 mm;
rostellum lobes mostly parallel, closely spaced, directed downward, very small, rounded, obscure;
pollinaria straight;
pollinia remaining enclosed in anther sacs;
viscidia evidently elliptic-oblong;
ovary rather slender to stout, mostly 4.5–11 mm.
= 42.
Platanthera orbiculata
Platanthera limosa
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.)
Platanthera limosa is traditionally distinguished from other slender-spurred plants and from P. sparsiflora by the presence on the lip of a median thickening that culminates in a small basal process. Although diagnostic when present, this feature is often obscure, especially in live material, and seems to be lacking in some plants. Platanthera limosa is most consistently separated from other green-flowered species by the combination of very small, narrow column and slender spur much longer than the lip. These features are in contrast to the very large, broad columns of P. sparsiflora and P. zothecina and much shorter spurs of the P. hyperborea complex. The lips of most plants are elliptic to elliptic-oblong, unlike any other species except the Aleutian P. tipuloides, and such plants are readily determined by lip shape and spur characters. Within populations plants may vary greatly in flower size, spur shape and length, and the ratio of spur to lip length. Individual plants may vary markedly in size of the flowers and density of the inflorescence in different years. That situation warrants additional study, as it may obscure the presence of other taxa.
(Discussion copyrighted by Flora of North America; reprinted with permission.)
- Local floras:
BC, 
WA - Local Web sites:
Flora NW, 
Go Botany, 
IL Wildflowers, 
MD Biodiversity, 
MI Flora, 
MN Wildflowers, 
PNW Herbaria, Turner Photog. 
WildflowerSearch
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USDA Plants Database- LBJ Wildflower Center
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