Philodendron: Difference between revisions

[[Sexual reproduction]] is achieved by means of [[beetles]], with many philodendron species requiring the presence of a specific beetle species to achieve pollination. The reverse is not always the case, as many beetle species will pollinate more than one philodendron species. These same beetles could also pollinate other genera outside of philodendron, as well as outside of the family [[Araceae]]. The pollinating beetles are males and members of the subfamily Rutelinae and [[Dynastinae]], and to date the only beetles seen to pollinate the inflorescence are in the genera ''[[Cyclocephala]]'' or ''[[Erioscelis]]''.<ref name="Gibernau4">{{harvnb|Gibernau|Barabé|Cerdan|Dejean|1999|p=1135}}</ref> Other smaller types of beetles in the genus'' Neelia'' visit the inflorescences, as well, but they are not believed to be involved in pollinating philodendrons. To attract the beetles, the sterile male flowers give off [[pheromones]] to attract the male beetles, usually at [[dusk]]. This process, female [[anthesis]], is followed by male anthesis, in which the pollen is produced. Female anthesis typically lasts up to two days and includes the gradual opening of the spathe to allow the beetles to enter. Some evidence suggests the timing of opening of the spathe is dependent on light levels, where cloudy, darker days result in the spathe opening up earlier than on clear days. During female anthesis, the spadix will project forward at roughly 45° relative to the spathe.

[[File:Imbé Philodendron byKoehne.jpg|thumb|right|''[[Philodendron bipinnatifidum ]]'' inflorescence]]

 

The male beetles will stay overnight in the spathe, eating and mating throughout the night due to the benefits provided by the spathe and spadix. Typically, five to 12 beetles will be within the spathe throughout the night. Rarely, cases of 200 beetles at a time have been observed and almost always the beetles are of the same species.<ref name="Gottsberger">{{harvnb|Gottsberger|Silberbauer-Gottsberger|1991|page=26}}</ref> Another feature of this symbiotic relationship, less well understood, is the series of events in which the spadix begins to heat up prior to the spathe opening up for the beetles. This process is known as [[Thermogenic plants|thermogenesis]].<ref name="Seymour1">{{harvnb|Seymour|Gibernau|2008|pp=1353–1354}}</ref> By the time the spathe is open and the beetles have arrived, the spadix is usually quite hot; up to around 46&nbsp;°C in some species, but usually around 35&nbsp;°C. The thermogenesis coincides with the arrival of the beetles and appears to increase their presence. The maximum temperature reached by the spadix remains about 20&nbsp;°C higher than the outside ambient temperature.<ref name="Nagy">{{harvnb|Nagy|Odell|Seymour|1972|page=1195}}</ref> The time dependence of the temperature can vary from species to species. In some species, the temperature of the spadix will peak on the arrival of the beetles, then decrease, and finally increase reaching a maximum once again when the philodendron is ready for the beetles to leave. Other species, though, only show a maximum temperature on the arrival of the beetles, which remains roughly constant for about a day, and then steadily decreases.<ref name="Gibernau">{{harvnb|Gibernau|Barabé|2000|pp=685–689}}</ref> A few species will show three peaks in temperature during the flowering. The increased temperature increases the metabolism of the beetles, causing them to move about more 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"/> The spadix has been shown to generate [[infrared radiation]]. As the beetles home in on the inflorescence, they first move in a zig-zag pattern until they get reasonably close, when they switch to a straight-line path. The beetles may be using scent to find the inflorescence when they are far away, but once within range, they find it by means of the infrared radiation. This would account for the two different types of paths the beetles follow.