Clubmosses represent an ancient lineage of vascular plants, having evolved approximately 410 million years ago. These plants are distinct from true mosses because they possess specialized tissues that transport water and nutrients, allowing them to grow larger. Modern clubmosses are low-growing, evergreen herbs that reproduce through spores rather than seeds. They often feature cone-like structures, known as strobili, where these spores are produced.
Defining Toothed Clubmoss
Toothed Clubmoss, scientifically known as Dendrolycopodium dendroideum, is an evergreen perennial plant often referred to by common names such as tree groundpine, round-branch clubmoss, or prickly tree-clubmoss. It is characterized by its tree-like growth form, with erect stems that reach heights of 12 to 30 centimeters. These stems arise from deeply buried horizontal underground stems called rhizomes, from which new shoots emerge.
The plant’s branches are multi-forked and round in cross-section, contributing to its miniature tree appearance. Its leaves are linear and sharp-tipped, measuring about 2 to 5.5 millimeters in length. They are arranged in 6 to 8 even rows that spiral around the stem, appearing as six distinct columns. The “toothed” appearance of Dendrolycopodium dendroideum is due to the sharp, prickly nature of the lower leaves on its upright stems, rather than serrated edges. Spores develop in stalkless, cone-shaped strobili, which are 1 to 6 centimeters long and appear singly or in clusters of one to seven at the branch tips. These spores are released from late summer into fall.
Habitat and Distribution
Toothed Clubmoss thrives in environmental conditions, preferring moist, well-drained, and acidic soils. It is found in forested habitats, including woodlands, open forests, and second-growth shrubby areas. The plant also grows on rock outcrops, talus slopes, or boulder fields that have a significant layer of moss and organic debris.
This species is well-adapted to cool, temperate climates and requires consistent moisture and high humidity. While it can tolerate a temperature range between 0°C (32°F) and 38°C (100°F), optimal growth occurs when temperatures are above 20°C (68°F). Dendrolycopodium dendroideum has a circumpolar distribution, extending across northern North America from Alaska to Newfoundland, and reaching south into states like Washington, Montana, Illinois, and Tennessee.
Ecological Significance and Distinguishing Features
Toothed Clubmoss serves as groundcover in forest environments. Its growth is slow, and it relies on a symbiotic relationship with mycorrhizal fungi for nutrients. The plant’s gametophyte stage, which is part of its reproductive cycle, is dependent on these fungi for survival. Ancestors of modern clubmosses were much larger, forming extensive forests that contributed to significant coal deposits over geological time.
Distinguishing Toothed Clubmoss from other clubmoss species involves observing several features.
- Its tree-like form, with erect, multi-forked stems.
- Lateral branches that are round in cross-section, differentiating it from species like Diphasiastrum complanatum with flattened branchlets.
- Linear, sharp-tipped leaves arranged in distinct rows, with lower leaves on the main stem being spreading and prickly (unlike Dendrolycopodium hickeyi which has more appressed lower stem leaves).
- Spreading via deeply buried horizontal rhizomes, contrasting with some clubmosses that spread through surface-level runners.
- Stalkless, cone-shaped strobili, found singly or in clusters at the plant’s apex.