Lycopodium obscurum
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''Dendrolycopodium obscurum'',
synonym A synonym is a word, morpheme, or phrase that means exactly or nearly the same as another word, morpheme, or phrase in a given language. For example, in the English language, the words ''begin'', ''start'', ''commence'', and ''initiate'' are all ...
''Lycopodium obscurum'', commonly called rare clubmoss, ground pine, or princess pine, 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 In the fields of horticulture and Botany, the term ''deciduous'' () means "falling off at maturity" and "tending to fall off", in reference to trees and shrubs that seasonally shed leaves, usually in the autumn; to the shedding of petals, afte ...
, 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.Family Lycopodiaceae, genus ''Lycopodium''; world species list
/ref>


Description

''Dendrolycopodium obscurum'' is known for the superficial resemblance of its
sporophyte A sporophyte () is the diploid multicellular stage in the life cycle of a plant or alga which produces asexual spores. This stage alternates with a multicellular haploid gametophyte phase. Life cycle The sporophyte develops from the zygote pr ...
to various conifers. However, its above-ground parts are rarely more than 15 cm (6 inches) tall. Its main stem is actually a
subterranean Subterranean(s) or The Subterranean(s) may refer to: * Subterranea (geography), underground structures, both natural and man-made Literature * ''Subterranean'' (novel), a 1998 novel by James Rollins * ''Subterranean Magazine'', an American fa ...
, creeping
rhizome In botany and dendrology, a rhizome (; , ) is a modified subterranean plant stem that sends out roots and shoots from its nodes. Rhizomes are also called creeping rootstalks or just rootstalks. Rhizomes develop from axillary buds and grow hori ...
, which grows about 6 cm (2.4 inches) below ground. Several aerial
shoots In botany, a plant shoot consists of any plant stem together with its appendages, leaves and lateral buds, flowering stems, and flower buds. The new growth from seed germination that grows upward is a shoot where leaves will develop. In the spri ...
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 Vegetative reproduction (also known as vegetative propagation, vegetative multiplication or cloning) is any form of asexual reproduction occurring in plants in which a new plant grows from a fragment or cutting of the parent plant or spec ...
, through its rhizome.Flora of North America, ''Lycopodium obscurum'' Linnaeus, 1753.
/ref> 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 Dendrochronology (or tree-ring dating) is the scientific method of dating tree rings (also called growth rings) to the exact year they were formed. As well as dating them, this can give data for dendroclimatology, the study of climate and atmos ...
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.


Taxonomy

The genus ''
Dendrolycopodium The genus ''Dendrolycopodium'' is a clubmoss genus in the family Lycopodiaceae. In the Pteridophyte Phylogeny Group classification of 2016 (PPG I), it is placed in the subfamily Lycopodioideae. Some sources do not recognize the genus, sinking it ...
'' is accepted in the
Pteridophyte Phylogeny Group The Pteridophyte Phylogeny Group, or PPG, is an informal international group of systematic botanists who collaborate to establish a consensus on the classification of pteridophytes (lycophytes and ferns) that reflects knowledge about plant relation ...
classification of 2016 (PPG I), but not in other classifications, which submerge the genus in '' Lycopodium''.


Uses and conservation

Historically, ''Dendrolycopodium obscurum'' has been
harvest Harvesting is the process of gathering a ripe crop from the fields. Reaping is the cutting of grain or pulse for harvest, typically using a scythe, sickle, or reaper. On smaller farms with minimal mechanization, harvesting is the most labor-i ...
ed 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 State law refers to the law of a federated state, as distinguished from the law of the federation of which it is a part. It is used when the constituent components of a federation are themselves called states. Federations made up of provinces, cant ...
. 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

{{Taxonbar, from1=Q15338742, from2=Q3281399 Lycopodiaceae Flora of China Flora of Eastern Asia Flora of North America Flora of the Russian Far East Plants described in 1753 Taxa named by Carl Linnaeus