Polypodium saximontanum

Stems often whitish pruinose, slender, to 6 mm diam., acrid-tasting; scales weakly bicolored, lanceolate, contorted distally, bases and margins light-brown, sometimes with dark central stripe, margins often coarsely dentate. Leaves to 25 cm. Petiole slender, to 1.5 mm diam. Blade oblong to linear, pinnatifid, usually widest near middle, to 4 cm wide, somewhat leathery; rachis sparsely scaly to glabrescent abaxially, glabrous adaxially; scales lanceolate-ovate, usually more than 6 cells wide. Segments oblong, less than 12 mm wide; margins entire to crenulate; apex rounded to broadly acute; midrib glabrous adaxially. Venation free. Sori midway between margin and midrib to nearly marginal, less than 3 mm diam., circular when immature. Sporangiasters present, usually less than 40 per sorus, heads with a few glandular-hairs or rarely without glands. Spores more than 58 µm, tuberculate, surface projections more than 3 µm tall. 2n = 148.

Phenology: Sporulating summer–fall.
Habitat: Cracks and ledges on rocks, apparently confined to granitic substrates
Elevation: 1800–3000 m

Colo., N.Mex., S.Dak., Wyo.

Discussion

Polypodium saximontanum is an allotetraploid species whose progenitor diploid species are P. amorphum and P. sibiricum (M. D. Windham 1993). Prior to its recognition as a distinct species, collections of P. saximontanum were variously referred to P. montense F. A. Lang (= P. amorphum), P. hesperium, and/or P. virginianum. In addition to its separate geographic range, P. saximontanum can be distinguished from P. virginianum by having narrower leaves and a reduced frequency of glandular hairs on its sporangiasters. Polypodium saximontanum also has a separate range from P. amorphum and has spores with large (greater than 3 µm tall) projections. Although P. saximontanum overlaps in range with P. hesperium, the latter species has no sporangiasters. Tetraploid hybrids of these two species have misshapen spores.

Selected References

None.

Lower Taxa