I first became interested in writing about this species when I watched Jonathan Drori’s TED talk: “The Beautiful Tricks of Flowers“. In this presentation, Jonathan explains that Philodendron bipinnatifidum‘s metabolism burns a substance very similar to the brown fat that mammals use, rather than the starch that most plants metabolize. This species does something else that is very unusual in the plant kingdom: not only can Philodendron bipinnatifidum produce heat, it can also regulate its heat production.
Philodendron bipinnatifidum, or tree philodendron, was featured on Botany Photo of the Day in 2008, following a lively discussion on the UBC Botanical Garden Forums. One of the forum participants had noticed that his potted Philodendron bipinnatifidum plant was giving off heat as well as having its spadix move throughout the day. The movement was presumably to orient itself so that the heat would be reflected back onto it from the concave spathe. It was a fascinating discussion (see the accompanying video of the spadix moving over the course of 8 hours), made all the more interesting when supported by an article that largely explains how and why this species produces heat.
Environmental biologist Roger S. Seymour studies the heat production of arums, and in an article published in 1999, he explains the four-day heat cycle of Philodendron bipinnatifidum (synonym Philodendron selloum). On the first day, heat production is only slightly above ambient air temperature, and the spathe loosens but does not open. By the evening of the second day, the spathe is fully open, and the inflorescence reaches temperatures of 38-46°C for a period of about two hours. Heat production then plateaus at 25-36°C and remains relatively constant throughout the third day. That afternoon the spathe closes, and in the evening, the spathe opens slightly and temperatures begin to decrease. During the final night, the spathe closes again, and temperatures return to that of the ambient air temperature.
Why all of these changes in temperature, and why the repeated opening and closing of the spathe, you ask? The answer to this question lies in the mating habits of a dynastid scarab beetle (either Erioscelis emarginata or Cyclocephala variolosa, depending on the subspecies of Philodendron bipinnatifidum). The two-hour period of maximum heat production is a signal; the high heat amplifies tree philodendron’s musky scent, and up to 200 dynastid scarab beetles are drawn to the inflorescence, clamouring for one of only 10-15 spots within the floral chamber. At this time, the female florets are receptive to pollination; an act that is likely to occur with so many (often already pollen-coated) beetles writhing against them. Next is a roughly 24 hour period of relatively stable, warm temperature, during which time the beetles are housed very comfortably. They are kept warm, fed nutritious secretions from the female florets, and are of course well-entertained by the other beetles in attendance (I am afraid to describe what happens within the floral chamber lest your web-filter deem our blog inappropriate content). Many of the beetles that secure a coveted spot within the floral chamber remain a full 24 hours. Once the party is over, the spathe begins to close. This squeezes the beetles out of the floral chamber, during which the beetles are coated in a resinous yellow fluid. The closing of the spathe is timed perfectly with the release of pollen, which adheres easily to the sticky beetles. The pollen-covered dynastid scarab beetles then sniff the air for the scent of the next Philodendron bipinnatifidum party, and the cycle is repeated.