Lycopodiella serpentina (Kunze) B.Øllg.

Horizontal stems dichotomously branching, prostrate and appressed to surface, rooting at intervals 8–30 mm apart, 1–2 mm diameter; leaves imbricate, ascending, linear to narrowly triangular, adnate. Aerial stems erect, unbranched, glabrous; longest fertile stems 15–140 mm tall (including strobili). Sterile leaves monomorphic, spirally arranged, appressed or spreading, linear to narrowly triangular, apices acuminate, margins entire but minutely ciliate at apex, bases adnate, 2.5–5.0 mm long, 0.4–1.0 mm wide, dull green or rarely tinged orange. Sporophylls appressed when young, spreading at maturity, narrowly ovate to ovate, apices acuminate, margins ciliate, bases adnate or subpeltate, 2.5–4.0 mm long, 1.0–1.8 mm wide, aggregated into strobili. Strobili solitary, terminal on branches, erect, sessile, yellow-green, 6–95 mm long, 5–8 mm wide.

Lycopodiella serpentina is distinguished by its appressed, prostrate, horizontal stems that root at intervals, and its unbranched aerial stems that terminate in solitary, unbranched strobili. The sterile leaves are also distinctive in having an ascending habit on the horizontal stems, but appressed or spreading on the aerial stems.

Lycopodiella serpentina grows firmly appressed to the ground in boggy areas, on peat, in poorly drained paddock, in gumland, and on sandy soils, often with Sphagnum and Empodisma or under stunted mānuka or Gleichenia.

The name Lycopodium carolinianum L. used in 19^th century New Zealand Flora treatments is a misidentification of Lycopodiella serpentina.

Øllgaard (1987) included both Lycopodiella serpentina and L. caroliniana within section Caroliniana (= Pseudolycopodiella Holub). However, Burnard et al. (2016) did not recover these two species as a clade, suggesting that some of the distinguishing morphological characters must be homoplastic within Lycopodiella, and that the current classification needs revision.