Witchwood is a magical vine of uncertain origin. It seems to be more prone to growing in climates which are mild year-round, as any place where the ground is subject to a hard freeze it is never found, and where the ambient humidity is generally over 70%. Its true method of propagation is a mystery, as it has never been observed to flower, but it has been observed that it has a profound ability to self-propagate through cuttings of the stem or root, with the most vigorous regrowth coming from the transplanted root crown. Functionally, this means that if the plant is cut off at ground level, the aerial vine can re-root just as readily as a new plant will grow from the underground roots still remaining, and if the vine is chopped up into small pieces, each piece has the potential to grow into a new, separate plant. Its aerial parts can be readily destroyed by burning, but as the roots remain untouched by fire, it will regrow.
For most of the year, it appears as just a thick mat of intertwined thin brown vines, forming what looks like a net which covers existing vegetation, as well as climbs up and over buildings and other artificial structures, choking out whatever it grows over. In fact, the vegetation it grows atop has the tendency to wither and die at a rate much faster than can usually be accounted for by simply light deprivation, which is in accordance with its most infamous observed property: its seeming tendency to draw the life energy from living things in its proximity. Its growth habit is usually that a cutting will first grow underground to establish a root system, and then send out a thin rhizome just under the surface, from which small suckers grow from which, in time, will result in a mass of anywhere between 1 and 6 vines. They spread out in all angles, growing around each other and climbing whatever obstacle is in their way, eventually growing small, simple, opposite, acuminate leaves, of a greenish-red color along the length of the new vine and then dropping after only a matter of a couple months. New vines grow from the tips of old vines, or else from any place where the vine is broken or cut, and only new growth gets leaves. Very old growth, that is, growth that is undisturbed for several years, can create very thick mats that are so tightly interwoven and layered that it creates a more or less steady surface that one can walk across without falling through. The youngest vine growth is nevertheless very brittle, and is easily snapped.
Though it prefers places of high humidity, moderate to high temperatures, and high light, it can occasionally be found growing in places with no light, as the vines can sometimes grow into or underneath something and be nourished by the other vines attached to their roots that are above ground. Over time, one can occasionally find startlingly large growths of witchwood in caves and abandoned buildings, as long as it has another source of nourishment at hand. Namely, sources of arcane energy. Therefore, in some places where there is a lot of magical activity, such as mages' towers and lichs' phylacteries, witch wood can grow very vigorously and even completely conceal the entrances or the entire structures.
Functionally, witchwood has its strongest effect on wizards and warlocks and those who use the arcane power source. Standing in a square occupied by witchwood, one suffers a -2 modifier on all rolls which use the arcane keyword. Furthermore, if someone drops to zero hit points in a square occupied by witchwood, they get a -2 modifier to their saving rolls, and others trying to help them get a -2 modifier on heal checks. Additionally, if an arcane character drops in a square containing witchwood, they take a -4 modifier on saving throws, as it is sucking away their arcane energy.
Lastly, witchwood, depending on the thickness of the mats, can be either difficult terrain or hindering terrain, tripping characters walking across it.