Leaves and stems:

Leaves are evergreen, appearing opposite but spirally arranged with 4 evenly spaced leaves in a cycle, appearing as 4 columns when viewed from the side of the stem (4-ranked). Branch leaves are green, somewhat shiny, the base extending down the stem (decurrent) and the free portion at the tip pointed and scale-like. Branches are rectangular in cross-section, flattened on the underside with the associated leaf much smaller than the rest.

Lateral leaves are largest, the free portion appressed to spreading, and the leaf on the upper surface appressed and more narrow. Horizontal stems are above ground or just below the surface of the duff layer. At fairly regular intervals, erect shoots emerge, each with 2 or more branches near the base. Branches are mostly ascending to spreading, forked and tree-like, mostly arranged on the same plane, fan-like. There is no distinct constriction where the annual bud grew. The erect shoots are 3 to 20 inches tall, though vegetative shoots are typically less than 8 inches.

Spores:

Spores develop in spike-like or cone-like structures called strobili, usually 2 to 4 strobili (rarely more) clustered at the tip of a long stalk (peduncle). Usually 2 peduncles rise up to 5 inches above the leaves, with appressed, scale-like leaves spiraling up at regular intervals. Strobili are 3/8 to 1½ inches long, each strobilus also distinctly stalked on forked branches. Strobili stalks are all about the same length but primary branches are minute, forking at or near the base, giving the appearance the strobili are whorled at the tip of the peduncle. Each tiny spore sac is attached to a scale (sporophyll) that is less than 1/8 inch (to 2.6mm) long, broadly diamond to heart-shaped and abruptly tapering to a pointed tip. Scales are initially light green and tightly appressed, turning yellowish as they mature and light brown when dry, then become more spreading to release the spores in late summer into fall. Scales at the tip of strobili are often sterile. The strobili can persist through winter.

Notes:

Southern Groundcedar reaches the western edge of its range in Minnesota, found in a variety of habitats from hardwood to pine forest, wooded slopes and ravines, margins of wet meadows, grassy ditches, and taconite tailings basins. It is among the species formerly all lumped into Lycopodium (L. digitatum or L. flabelliforme), which many references have now split into several genera and we have followed suit. Distinguishing characteristics of the new groups are: whether spores develop in cone-like strobili or in leaf (or leaf-like) axils, whether strobili are stalked or stalkless, whether horizontal stems are above or below ground, whether branching on erect shoots is tree-like or not, the number of leaves in a spiral cycle, whether leaves are scale-like or not and whether they have a hair-like tip. The Diphasiastrum species all have stalked strobili, tree-like branching, leaves that are scale-like, 4-ranked and lack a hair-like tip. The tree-like branching and scale-like leaves resemble little cedar trees and is why they are commonly called groundcedars.

Southern Groundcedar is distinguished by horizontal stems that are above ground or just below the surface of the duff layer, 2 to 4 strobili (rarely more) that appear nearly whorled at the tip of the peduncle, strobili tips often with sterile scales, branchlets rectangular in cross-section and without obvious annual constrictions, the underside distinctly flattened with the associated leaf much smaller than the others, and upper branches that are strongly fan-like, the branchlets mostly all on the same plane (like fingers on a hand). The branch arrangement and branchlet shape can help identify it even when strobili are not present. Southern Groundcedar is very similar to Northern Groundcedar (D. complanatum), which also has flattened branchlets but they have obvious annual constrictions, its branches are not strongly fan-like, and has 1 to 4 strobili (rarely more) on more obviously forking branches, and strobili tips are not sterile. For a time D. digitatum was treated as a variety of D. complanatum (var. flabelliforme). These two species are known to hybridize and the hybrid is easily confused with either parent.

The other Diphasiastrum species in Minnesota, Blue Groundcedar (D. tristachyum), has horizontal stems 2+ inches below ground, branches are more blue-green and have branchlets that appear more square in cross-section, the leaves on all 4 sides all about the same size. Compare with other clubmosses with cone-like strobili: Spinulum species have stalkless strobili and lack tree-like branching, Lycopodium have stalked strobili but lack tree-like branching, and Dendrolycopodium have tree-like branching but stalkless strobili single at branch tips, and none of these have scale-like leaves. D. tristachyum hybridizes with both of Minnesota's other groundcedars, the hybrid with D. complanatum (D. ×zeilleri) most common and with D. digitatum (D. ×habereri) less so. Descriptive information on all these hybrids is not well documented but intermediate characteristics are likely.