Philodendron is a large genus of flowering plants from the arum family (Araceae), consisting of close to 900 or more species according to TROPICOS (a service of the Missouri Botanical Garden). Other sources quote different numbers of species. According to S.J. Mayo there are about 400 formally recognized species whereas according to Croat there are about 700. Whichever the exact number of species, the genus is the second largest member of the arum family. Taxonomically the genus Philodendron is still poorly known with many undescribed species. Many are grown as ornamental and indoor plants. The name derives from the Greek philo or "love" and dendron or "tree".

Distribution

Philodendron species can be found in many diverse habitats in the tropical Americas and the West Indies. Most occur in humid tropical forests, but can also be found in swamps, on river banks, roadsides and rock outcrops. They are also found throughout a diverse range of elevations from sea level to over 2000 meters. Species of this genus are often found clambering over other plants, or climbing the trunks of other trees with the aid of aerial roots. Philodendron usually distinguish themselves in their environment due to their large numbers compared to other plants making them a highly noticeable component of the ecosystems they're found in. Additionally, they are found in great numbers on the sides of road clearings.

Philodendrons can also be found in Australia, some Pacific islands, and Asia although they aren't indigenous to these regions. Rather they were introduced or accidentally escaped.

Growth Habit

Compared to other genera of the family Araceae, Philodendron have an extremely diverse array of methods by which they grow. The habits of growth can be epiphytic, hemiepiphytic, or terrestrial although very few Philodendrons grow terrestrially. Others can show a combination of these growth habits depending on the environment the plant is in. Hemiepiphytic Philodendron can be classified into two types, primary and secondary hemiepiphytes. The primary hemiepiphytic Philodendron start their life high up in the canopy where the seed initially sprouts. The plant then grows as an epiphyte gaining size and then once it has reached a sufficient size and age, it will begin producing aerial roots that grow towards the forest floor. Once the roots have reached the forest floor, nutrients can be obtained. In this manner the plants strategy is to obtain light early in its life at the expense of nutrients. Some primary epiphytic species have a symbiotic relationship with ants. In these species the ant's nest is grown amongst the roots of the Philodendron and help keep the nest together. Additionally, Philodendron have extra floral nectaries that secretes nectar that attracts the ants. The Philodendron in tern obtains nutrients from the surrounding ant nest and the aggressive nature of the ants serves to protect it against other insects who would choose to eat it. Secondary hemiepiphytes start their life off on the ground or on part of a tree trunk very close to the ground where the seed sprouts. For these Philodendron they have their roots in the ground early on in their lives. They then begin climbing up a tree and eventually may become completely epithytic by doing away with their subterranean roots. Secondary hemiepiphytes don't always start off their lives close to a tree. For these Philodendron what happens is that the plant will grow with long internodes along the ground until a tree is found. They find a suitable tree by means of growing towards darker areas since trees produce a dark shadow. This trait is called scototropism. After a tree has been found the scototropic behavior stops and the Philodendron switches to a heliotropic growth habit and shortens the internodes and makes them thicker. Usually however Philodendron germinate on trees.