Appearance
"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 tall. Its main stem is actually a subterranean, creeping rhizome, which grows about 6 cm 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 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 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.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.
Status
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. While flash powder is now practically obsolete, the harvest of "D. obscurum" has caused it to become threatened in several areas, leading Indiana and New York to declare it protected by state law. When harvesting legally, it is recommended to cut the shoots using shears to minimize rhizome damage, alternate sites every year, and select only individuals possessing strobili with open sporophylls. This ensures that immature shoots are not harvested, and will be allowed an attempt at reproduction.
Uses
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. While flash powder is now practically obsolete, the harvest of "D. obscurum" has caused it to become threatened in several areas, leading Indiana and New York to declare it protected by state law. When harvesting legally, it is recommended to cut the shoots using shears to minimize rhizome damage, alternate sites every year, and select only individuals possessing strobili with open sporophylls. This ensures that immature shoots are not harvested, and will be allowed an attempt at reproduction.References:
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