Editing Philodendron (section)

==Description==

===Growth habit===
Compared to other genera of the family [[Araceae]], philodendrons have an extremely diverse array of growth methods. The habits of growth can be [[epiphyte|epiphytic]], [[hemiepiphyte|hemiepiphytic]], or rarely [[terrestrial plant|terrestrial]].<ref name="Croat2">{{harvnb|Croat|1985|p=252 }}</ref> Others can show a combination of these growth habits depending on the environment. Hemiepiphytic philodendrons can be classified into two types: primary and secondary hemiepiphytes. A primary hemiepiphytic philodendron starts life high up in the canopy where the seed initially sprouts. The plant then grows as an epiphyte. Once it has reached a sufficient size and age, it will begin producing aerial roots that grow toward the forest floor. Once they reach the forest floor, nutrients can be obtained directly from the soil. In this manner, the plant's strategy is to obtain light early in its life at the expense of nutrients. Some primary epiphytic species have a [[symbiotic relationship]] with ants.<ref name="Yu">{{harvnb|Yu|1994|pp=222–223 }}</ref> In these species, the ants' nest is grown amongst the plant's roots, which help keep the nest together. Philodendrons have [[Extrafloral nectary|extrafloral nectaries]], glands that secrete nectar to attract the ants. The philodendron, in turn, obtains nutrients from the surrounding ant nest, and the aggressive nature of the ants serves to protect the plant from other insects which would eat it.<ref name="Gibernau3">{{harvnb|Gibernau|Orivel|Dejean|Delabie|2008|p=689 }}</ref>

Secondary hemiepiphytes start life on the ground or on part of a tree trunk very close to the ground, where the seeds sprout. These philodendrons have their roots in the ground early in their lives. They then begin climbing up a tree and eventually may become completely epiphytic, doing away with their subterranean roots. Secondary hemiepiphytes do not always start their lives close to a tree. For these philodendrons, the plant will grow with long [[internode (botany)|internodes]] along the ground until a tree is found. They find a suitable tree by growing towards darker areas, such as the dark shadow of a tree. This trait is called scototropism. After a tree has been found, the scototropic behavior stops and the philodendron switches to a [[phototropism|phototropic]] growth habit and the internodes shorten and thicken. Usually, however, philodendrons germinate on trees. A few species, such as ''[[Philodendron fragrantissimum]]'' switch repeatedly between globular clumps of leaves with very short [[internodes]] and naked internodes of uncommon length (up to a yard (meter) or more) followed by another clump and so on.<ref>{{ cite book |last=Bown |first=Deni |date=2000 |title=Aroids - Plants of the Arum Family |location=Portland, Oregon |publisher=Timber Press |page=213 |ISBN=978-1-60469-201-3 }}</ref> ''[[Philodendron linnaei]]'' is another such species.

A few species show three peaks in temperature during flowering, which stimulates beetles within the spathe and increasing the likelihood they will be sufficiently coated with pollen. A sticky resin is also produced in drops attached to the spadix which help to keep the pollen attached to the beetles.<ref name="Barabé2">{{harvnb|Barabé|Gibernau|Forest|2002|p=81 }}</ref> This resin producing quality is unique to ''Philodendron'' and ''[[Monstera]]'', as other genera of [[Araceae]] do not produce it on their spadices. The resin is also found on the stems, leaves, and roots of philodendrons. Its color can be red, orange, yellow, or colorless when it is first produced. Yet, over time, it will turn brown as it is exposed to air. Also, some evidence suggests the thermogenesis triggers the beetles to mate. It also appears to distribute the pheromones into the air. The reason for the spadix being held at 45° relative to the spathe may be to maximize the heat's ability to waft the pheromones into the air. Oxidizing stored carbohydrates and lipids has been found to be the energy source for thermogenesis. The part of the spadix that heats up is the sterile zone. As it heats up, carbohydrates are used, but once the spadix has reached its maximum temperature, lipids are oxidized. The lipids are not first converted to carbohydrates, but rather are directly oxidized. The thermogenic reaction is triggered when concentrations of acetosalicytic acid form in the sterile zone. The acid sets off the [[mitochondria]] in the cells that make up the sterile zone to switch to an [[electron transport chain]] called the cyanide-resistant pathway, which results in the production of heat. Philodendrons consume [[oxygen]] during thermogenesis. The rate at which oxygen is used is remarkably high, close to that of [[hummingbirds]] and [[sphinx moths]].<ref name="Nagy">{{harvnb|Nagy|Odell|Seymour|1972|page=1195 }}</ref> The spadix has been shown to generate [[infrared radiation]].

===Leaves===
[[File:PhilodendronMaximum.jpg|thumb|right|A leaf of ''[[Philodendron maximum]]'']]
The leaves are usually large and imposing, often lobed or deeply cut, and may be more or less [[pinnate]]. They can also be oval (''Philodendron'' 'White Princess'), spear-shaped, divided (''[[Philodendron tripartitum]]'') or in many other possible shape variations. The leaves are borne alternately on the stem. A quality of philodendrons is that they do not have a single type of leaf on the same plant. Instead, they have juvenile leaves and adult leaves, which can be drastically different from one another. The leaves of seedling philodendrons are usually heart-shaped early in the life of the plant. But after it has matured past the seedling stage, the leaves will acquire the typical juvenile leaf's shape and size. Later in the philodendron's life, it starts producing adult leaves, a process called [[metamorphosis]].<ref name="Ray">{{harvnb|Ray|1990|pp=1599–1609 }}</ref> Most philodendrons go through metamorphosis gradually; there is no immediately distinct difference between juvenile and adult leaves.<ref name="Bell">{{harvnb|Bell|Bryan|2008|p=26 }}</ref> Aside from being typically much bigger than the juvenile leaves, the shape of adult leaves can be significantly different. In fact, considerable taxonomic difficulty has occurred in the past due to these differences, causing juvenile and adult plants to mistakenly be classified as different species.

The trigger for the transformation to adult leaves can vary considerably. One possible trigger is the height of the plant. Secondary hemiepiphytes start off on the dark forest floor and climb their way up a tree, displaying their juvenile type leaves along the way. Once they reach a sufficient height, they begin developing adult type leaves. The smaller juvenile leaves are used for the darker forest floor where light is in scarce supply, but once they reach a sufficient height in the canopy the light is bright enough that the bigger adult leaves can serve a useful purpose. Another possible trigger occurs in primary hemiepiphytes. These philodendrons typically send their aerial roots downward. Once their roots have reached the ground below, the plant will begin taking up nutrients from the soil, of which it had been previously deprived.<ref name="Orihuela1">{{harvnb|Orihuela|Waechter|2010|pp=119–122 }}</ref> As a result, the plant will quickly morph into its adult leaves and gain in size dramatically. Another quality of philodendrons leaves is they are often quite different in shape and size even between two plants of the same species. As a result of all these different possible leaf shapes, it is often difficult to differentiate natural variations from [[morphogenesis]].

===Cataphylls===
Philodendrons also produce [[cataphyll|cataphylls]], which are modified leaves that surround and protect the newly forming leaves. Cataphylls are usually green, leaf-like, and rigid while they are protecting the leaf. In some species, they can even be rather [[succulent]]. Once the leaf has been fully formed, the cataphyll usually remains attached where the stem and base of the leaf meet. In philodendrons, cataphylls typically fall into two categories: [[deciduous]] and persistent types.<ref name="Croat3">{{harvnb|Croat|1985|pp=253–254 }}</ref> A deciduous cataphyll curls away from the leaf once it has formed, eventually turning brown and drying out, and finally falling off the plant, leaving a scar on the stem where it was attached. Deciduous cataphylls are typically found on vining philodendrons, whereas persistent cataphylls are typical of epiphytic philodendrons or appressed climbers. In the latter, the cataphylls are prevented from falling off in a timely manner due to the short [[internodes]] of the plant. The cataphylls will remain attached, drying out and becoming nothing more than fibers attached at the nodes. In some philodendrons, the cataphylls build up over time and eventually form a wet mass at the nodes. This may keep emerging roots moist and provide some form of lubrication to new leaves.

===Roots===
Philodendrons have both [[aerial roots|aerial]] and subterranean roots. The aerial roots occur in many shapes and sizes and originate from most of the plant's [[node (botany)|nodes]] or occasionally from an internode. The size and number of aerial roots per node depends on the presence of a suitable substrate for the roots to attach themselves. Aerial roots serve two primary purposes. They allow the philodendron to attach itself to a tree or other plant, and they allow it to collect water and nutrients. As such, the roots are divided [[morphology (biology)|morphologically]] into these two categories. Aerial roots used for attaching to trees tend to be shorter, more numerous, and sometimes have a layer of root hairs attached; those used for collecting water and nutrients tend to be thicker and longer. These feeder roots tend to attach flush with the substrate to which the philodendron is attached, and make their way directly downwards in search of soil. In general, feeder roots tend to show both positive [[hydrotropism|hydrotropic]] and negative [[heliotropic]] behaviors. Characteristic of roots in philodendrons is the presence of a sclerotic hypodermis, which are cylindrical tubes inside the [[epidermis (botany)|epidermis]] that can be one to five cells long.<ref name="French1">{{harvnb|French|1987|pp=891–903 }}</ref> The cells that line the sclerotic hypodermis are elongated and tend to be hardened. Underneath the epidermis is a unique layer of cells in a pattern of long cells followed by short cells.

===Extrafloral nectaries===
Some philodendrons have extrafloral nectaries (nectar-producing glands found outside of the flowers). The nectar attracts ants, with which the plant enjoys a protective symbiotic relationship.<ref name="Blüthgen">{{harvnb|Blüthgen|Verhaagh|Goitía|Jaffé|2000|pp=229–240 }}</ref> Nectaries can be found in a variety of locations on the plant, including the [[plant stem|stalks]], sheaths, lower surfaces of the leaves, and [[spathe]]s. The nectaries produce a sweet, sticky substance the ants like to eat and which provides an incentive for them to build their nests amongst the roots of the given philodendron. In some cases, the amount of [[nectar]] produced can be quite extensive, resulting in the surface becoming entirely covered with it.