Horizontal stems mainly shallowly buried, 0.5--3 mm wide, sometimes emerging, 1.1--2.2 mm wide; leaves appressed, spatulate to lanceolate, 1.5--3.8 X 0.5--1.4 mm, apices truncate. Upright shoots 6--14 cm, clustered, fasciculate, branching successively 3--5 times; leaves on upright main stem ascending, deltate-ovate, 3.5--4 X 0.8 mm, apices needlelike. Branchlets square in cross section, 1.8--4 mm wide, annual bud constrictions abrupt and conspicuous; underside often glaucous, concave; upperside green, dull to faintly shiny, convex. Leaves on branchlets 4-ranked, overlapping; upperside leaves appressed, lanceolate, 3--5.8 mm, free portion of blades 1.7--2.9 X 0.1--1.1 mm; lateral leaves strongly divergent, 3.3--6.5 X 1.8--2.4 mm, margins revolute; underside leaves well developed, perpendicular to stem, 1.3--3.3 X 0.6--1.3 mm, unique in genus in having base contracted, blade flaring, and margins becoming parallel. Peduncles absent. Strobili solitary, 5--30 X 2--4 mm, sterile tips absent. Sporophylls deltate to nearly cordate, 2.2--3.5 X 1.6--3 mm, apices gradually tapering. 2 n = 46. The branchlet leaves of Diphasiastrum alpinum are unique in the genus, and the trowel-shaped underside leaves with their flared and rolled blades and contracted bases are particularly unusual. The leaves of the other North American species are much simpler in shape and contour.
Much like no. 13 [Lycopodium stitchense Rupr.], but the lvs of the ultimate vegetative branchlets strictly 4-ranked, decussately opposite, subtrimorphic; every other pair of lvs conspicuously decurrent on the stem as a pair of flanges, the flange continuous with one margin of the lf, so that the stem appears somewhat flattened or wing-margined with the lvs of the lateral rows twisted; free tips of these lateral lvs mostly 1.5-2 mm; dorsal and ventral lvs distinctly different from the lateral ones and also different inter se, those of the upper side subulate, straight, loosely appressed or closely ascending, 2-3 mm, shortly decurrent, those of the lower side (which appears to be concave because of the way the lateral lvs are twisted) tending to have a short, stout, ascending-spreading subpetiolar base (this often laterally compressed) and an erect (parallel to the stem) or incurved blade 2-3 mm and lanceolate or lance-ovate; 2n=46. Cold woods and subalpine meadows and rocky slopes; circumboreal, s. to Keweenaw Co., Mich. and the Gasp顰enins. of Que.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.