''Diphasiastrum tristachyum'', commonly known as blue clubmoss, blue ground-cedar, ground pine, deep-rooted running-pine or ground cedar, is a North American and Eurasian species of

clubmoss Lycopodiopsida is a class of vascular plants known as lycopods, lycophytes or other terms including the component lyco-. Members of the class are also called clubmosses, firmosses, spikemosses and quillworts. They have dichotomously branching s ...

. In North America, it has been found from Newfoundland west to Manitoba, and south as far as Georgia and Alabama. In Eurasia, it ranges from southern Norway and Sweden south to France and Italy and it also occurs in the Caucasus. The name tristachyum means three branched.

Description

''Diphasiastrum tristachyum'' is a

perennial A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also wide ...

species of clubmoss. It grows from creeping underground stems which are often deeply buried at 5–12 cm deep; at nodes from this stem the above ground stems emerge. The upright stems can be tall or higher. From the main stem, several fan shaped "leaves" emerge, these are not true leaves but rather branched stems which appear to almost look like leaves, each branches 4-6 times. The stems all grow to a similar height at the top of the plant, giving it a flat topped appearance which is a diagnostic character for this species. The peduncle is ~9 cm long and often branches twice near the top to form four

strobili A strobilus (plural: strobili) is a structure present on many land plant species consisting of sporangia-bearing structures densely aggregated along a stem. Strobili are often called cones, but some botanists restrict the use of the term cone to th ...

; the strobili are ~6 cm long and 3-4mm in diameter with a rounded tip. The strobili contain the

sporophyll A sporophyll is a leaf that bears sporangia. Both microphylls and megaphylls can be sporophylls. In heterosporous plants, sporophylls (whether they are microphylls or megaphylls) bear either megasporangia and thus are called megasporophylls, or mi ...

which are 2.2-3.5 X 1.6-3mm in size, light yellow, deltoid shaped, with a long sharp pointed tip, the edges are rough and chaffy; the spore case is almost round and the spores themselves are convex on their sides. The branches are 1-2.2mm wide and square with rounded angles when viewed in cross-section. The blue-green leaves are scale like, four-ranked and

lanceolate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...

subulate The following is a list of terms which are used to describe leaf morphology in the description and taxonomy of plants. Leaves may be simple (a single leaf blade or lamina) or compound (with several leaflets). The edge of the leaf may be regular o ...

. It can be distinguished from similar species by annual constrictions along these branches. Ground cedar prefers dry and sandy areas with poor soils, this allows it to grow in barrens and other xeric sites. It can tolerate sterile acidic soils which are often found within coniferous forests. Ground cedar also prefers to grow in open areas where other plants are not growing densely. Plants growing in the shade are more diffusely branched than those which grow in bright sun, but branchlets are always more rounded than those of either '' D. complanatum'' or '' D. digitatum''. Diphasiastrum tristachyum 240813d

Hybrids

''D. tristachyum'' forms many hybrids with other species in the genus ''Diphasiastrum'' *''Diphasiastrum × zeilleri'' (Rouy) Holub ('' D. complanatum X tristachyum'') is a frequent plant in areas of distributional overlap between the parents, especially in north central and western Minnesota jackpine forests. *''Diphasiastrum × habereri'' (House) Holub ('' D. digitatum X tristachyum'') has been overlooked and confused with both parents in zones of overlap. It is found occasionally to frequently in habitats like those of the parents, not necessarily growing close to them. *''Diphasiastrum × issleri'' (Rouy) Holub ('' D. alpinum X tristachyum'') is a rare hybrid in North America, reported only from Maine, but much more widespread in Europe. *''Diphasiastrum × sabinifolium'' (Willdenow) Holub ('' D. sitchense X tristachyum'') is widespread and frequent in eastern Canada. This hybrid is commonly confused with D . sitchense . It is highly variable, and some individuals approach one or the other parent in morphology (W. J. Cody and D. M. Britton 1989).

References

{{Taxonbar, from=Q245842 tristachyum Flora of North America Flora of Europe Flora of Asia Plants described in 1813