Other names for flat-Branched Tree-Clubmoss (Dendrolycopodium obscurum) are “Princess Pine” and “Ground Pine.” The name “Ground Pine” describes how the plant resembles a small pine tree. Flat-Branched Tree-Clubmoss grows in forests and wetlands. Flat-Branched Tree-Clubmoss is often cultivated in terrariums.
I. Appearance and Characteristics
Dendrolycopodium obscurum, synonym Lycopodium obscurum, commonly called rare clubmoss, ground pine, or princess pine, flat-Branched Tree-Clubmoss, is a North American species of clubmoss in the family Lycopodiaceae. It is a close relative of other species such as D. dendroideum and D. hickeyi, also treelike. It is native to the eastern United States and southeastern Canada from Georgia to Minnesota to Nova Scotia. It grows in the understory of temperate coniferous and deciduous forests, where it is involved in seral secondary succession, growing in clonal colonies some years after disturbance has occurred. It has also been found in Japan, Taiwan, Korea, Russian Far East, and northeastern China.
Dendrolycopodium obscurum is known for the superficial resemblance of its sporophyte to various conifers. However, its above-ground parts are rarely more than 15 cm (6 inches) tall. Its main stem is actually a subterranean, creeping rhizome, which grows about 6 cm (2.4 inches) below ground. Several aerial shoots branch off of the rhizome, which also branch dichotomously several times, giving D. obscurum its distinctive appearance. Fertile shoots possess sessile strobili, borne at the tops of their main axes and sometimes at the tips of dominant lateral branches.
The leaves are microphylls, each containing only a single vein and measuring less than 1 cm (0.4 inches) long. Two types of microphylls are formed, green trophophylls that cover most of the aerial shoots, and yellow to tan sporophylls that form the strobili, and contain the sporangia. D. obscurum reproduces sexually via spores and also vegetatively, through its rhizome.
The gametophyte of D. obscurum is disc shaped prothallus, measuring an average of 1.5 cm (0.6 inches) in diameter. It closely resembles other gametophytes of Lycopodium and related genera, so it cannot be identified by gametophyte alone. Doing so would be difficult nonetheless, as this type of gametophyte grows only underground, years after a disturbance has taken place. Therefore, the compact soil caused by repeated human traffic would disturb these areas, causing D. obscurum spores not to germinate and existing gametophyes to be damaged or killed.
- Identification
Identifying D. obscurum in the wild can be difficult without prior study, because it is not only relatively rare, but shares much of its morphology with D. dendroideum and D. hickeyi. However, it can be identified with the naked eye by observing its leaves. Below its first branch, the microphylls of D. obscurum are tightly packed to the axis, while those of D. dendroideum are fully spread down to the soil. The leaves on lateral branches of D. dendroideum and D. hickeyi are evenly shaped and distributed, while they are pressed into the horizontal plane in D. obscurum, with the underside leaves being much shorter than all others.
- Growth pattern
The rhizome of D. obscurum typically produces only one upright shoot per year and grows in a single direction. In the beginning of a growing season, the rhizome grows a few centimeters and then forms one branch at a 90° angle, alternating sides each year, which remains only millimeters in length. It then grows another couple of centimeters and then again branches off to the same side to form an aerial shoot. The rhizome branch produced each year is usually very weak and dies the next, but serves as a reserve rhizome apex, with the potential to become a new main rhizome. This happens if the plant is especially productive, or more frequently if the tip of the main rhizome is damaged so that it cannot grow.
When a new main rhizome is formed, it makes a second 90° turn so that it is growing in the same direction as the rhizome from which it came. All underground branching occurs parallel to the ground, so upright shoots must then orient themselves appropriately in order to emerge from the soil.
Every year, a main rhizome produces only one aerial shoot, but in the case of a plant with multiple main rhizomes a new shoot is produced from each. The age of a shoot corresponds to the layers of compressed microphylls in its stem, caused by growth halting each winter, the same way as tree rings are formed. Shoot morphology can also be used to estimate their ages.
First year shoots are unbranched and usually do not penetrate the soil surface. Second year shoots undergo rapid growth, usually reaching near their final heights, and forming several systems of lateral branches. Branching occurs only in the second, and sometimes third years. Strobili can be formed as early as the second growing season, but usually begin to be produced in the third. Strobilus production can continue through the fourth year, and shoots die in either the fourth or fifth year.

II. How to Grow and Care
Flat-Branched Tree-Clubmoss thrives in moist, well-drained soil, with a preference for partial to full shade, making it suitable for understory conditions or shaded garden areas. Special care should be taken to ensure consistent soil moisture without waterlogging, as flat-Branched Tree-Clubmoss is sensitive to both drought and excessive wetness. Its ease of care is attributed to its adaptability to various soil types, provided they are kept consistently moist.
Sunlight
Flat-Branched Tree-Clubmoss thrives in partial sun conditions, benefiting from a balance of sunlight and shade. This level of light is crucial for the flat-Branched Tree-Clubmoss’s photosynthetic process, directly influencing its growth and vitality. While flat-Branched Tree-Clubmoss tolerates full shade, extended periods in such low light can impair its development and may lead to diminished health. In its preferred outdoor habitat, flat-Branched Tree-Clubmoss should be planted in locations where dappled sunlight can reach it, emulating the light filtering effect of forest canopies.
Adaptive traits such as leaf adjustments may occur to optimize light absorption. Flat-Branched Tree-Clubmoss is typically not an indoor plant, thus indoor planting advice is not necessary.
Watering
Flat-Branched Tree-Clubmoss thrives in the understory of cool, temperate forests, where moisture is consistent but not excessive. This species exhibits a preference for evenly moist soil conditions and demonstrates moderate drought tolerance once established.
For optimal health, flat-Branched Tree-Clubmoss should be watered once every 2-3 weeks, allowing the soil to dry slightly between watering sessions. Typically grown outdoors due to its affinity for forest-like environments, flat-Branched Tree-Clubmoss benefits from mulching which helps retain soil moisture and mimics its natural habitat.
Fertilizing
For flat-Branched Tree-Clubmoss, use balanced nutrition fertilizers during active growth and high nitrogen types in the early stages to support lush foliage. Fertilize bi-monthly; a light, diluted solution is best. Fertilization enhances vigor and robustness. Seasonally adjust: less in winter. Precaution: avoid over-fertilization to prevent root burn. Tip: water soil before application to aid absorption.
Propagation
Flat-Branched Tree-Clubmoss is a perennial clubmoss thriving in woodland environments. It reproduces asexually through clonal growth and sexually by spores. Practical tips for propagating include ensuring moisture-rich, well-drained soil and providing a steady temperature. For successful sowing, spores should be spread on the surface of a peat-based substrate, avoiding burying as light aids germination. Patience is crucial as flat-Branched Tree-Clubmoss may be slow to establish, but with consistent care and attention to humidity, propagators can foster healthy growth.
Transplanting
To best establish flat-Branched Tree-Clubmoss, transplant it during the gentler intervals of growth in late spring’s warmth or autumn’s cool embrace, ensuring it’s nestled in well-draining soil with dappled shade. Embrace these times for their mild temperatures and optimal root development.
III. Uses and Benefits
Historically, Dendrolycopodium obscurum has been harvested from the wild for use as Christmas greens for wreaths, as well as the use of its spores for flash powder.