Bromeliads are all herbaceous, not woody, and most are easily recognize as bromeliads, and yet there is remarkable variation, since they range from pineapples (Ananas comosus) to rosettes of leaves with a water-collecting "tank" in the center which grow on the ground or high in trees, to "air plants" which take their water and nutrition out of the air, to strange shapes like Spanish moss (Tiliandsia usneoides).
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| bromeliads in tree |
Many bromeliads are epiphytes. An epiphyte is a plant that lives on other plants but is not parasitic. In the wet tropics, a plant on a branch of a tall tree can gather all the water it needs from rain and the necessary nutrients fall on it (leaves, dead insects, bird feces etc.). It is difficult to grow big on nutrients that fall from the sky, but it is a living.
The ancestors of bromeliads were likely ground-dwelling plants of dry environments. Moving into the trees, some bromeliad lineages have reduced roots until they no longer absorb nutrients and water but only secure the plant to the tree. Others have fused the central group of leaves so that water pools in a tank. In a humid climate, that tank can stay wet for weeks, allowing mosquitos and other water-using animals, including frogs, to lay their eggs and develop in the tank, all of which defecate useable nutrients into the tank, which absorbtive cells retrieve for the bromeliad. In some species, the leaves of the tank are vertical, so the tank is a death trap, collecting all the nutrients of its victims. Some bromeliads are so reduced that there is no tank; the leaves take up nutrients and water from the air. (Land-dwelling temperate humans don't realize how messy and busy trees can be. At the middle of a 100' tropical tree, leaves of the tree, its epiphytes, vines, mosses, and fungi fall onto and past the bromeliad. Ants, spiders, katydids, all kinds of flying and crawling insects stop to investigate it, frogs, lizards, snakes, rodents, dozens of species of birds, sloths, cats such as margays, monkeys all pass beside and above it. Lots of opportunity to catch nutrients.)
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| Bromeliads on tall tree (photos of bromeliads on high branches are difficult from the ground.) |
Most bromeliads are tough, able to endure for days or weeks with inadequate water or nutrients. About half of them have CAM (crassulacean acid metabolism) which allows them to keep their stomates (pores in the leaves) closed in the heat of the day, opening in the cooler nighttime to do photosynthesis, conserving water.
Typically bromeliads are a rosette (circle) of leaves, growing slowly bigger for a long time. When the plant has stored enough energy to flower, it sends up an often spectacular flowering stalk. If you live quietly on a tree branch, a big advertisement to get pollinators to visit can be important. Most are pollinated by animals, from bees to hummingbirds, and the seeds are in fruits that animals will disperse.
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| bromeliad in flower (set on a tree in a Costa Rica garden) |
Comments and corrections welcome.
References
Judd, W.S., C. S. Campbell, E. A. Kellogg, P. F. Stevens, and M J. Donoghue. 2008. Plant Systematics 3rd ed. Sinauer Associates, Sunderland MA.
Stevens, P. F. (2001 onwards). Angiosperm Phylogeny Website. Version 14, July 2017 [and more or less continuously updated since]." http://www.mobot.org/MOBOT/research/APweb/. Accessed 7/19/20.
Kathy Keeler, A Wandering Botanist
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Very interesting overview! What a neat family.
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