fall 2016 29 Many palms are known to be litter-trappers, and several in-depth studies of litter-trapping have focused on litter-trapping palms. Some palms trap and retain litter in their leaf crowns; a few even hold water, like bromeliads. Salacca magnifica, Sommieria leucophylla, Calyptrogyne ghiesbreghtiana and Johannesteijsmannia altifrons (all in the Tropical Plant Conservatory) are all consummate litter-trappers, although the roof of the Conservatory prevents them from naturally catching litter in their crowns. Other palms use another litter-trapping strategy, funneling litterfall toward the center of their crowns, where the litter drops to the ground below, forming a compost pile directly around the base of the trunk. An example of this kind of littertrapping palm can be found among the many forest species of Licuala. I have seen Licuala species in Malaysian rainforests with the telltale mound of leaf litter heaped around their short trunks, augmenting the leaf litter that carpets the forest floor. Just outside the Conservatory, you can see some young plants of Clavija domingensis and Theophrasta jussieui (both Primulaceae) grown from seeds collected by the Garden’s staff in the Dominican Republic. The genus Clavija comprises some 55 species from the American tropics, and all of them are litter-trappers. Theophrasta has just two species from Hispaniola, and both are litter-trappers. These are small trees with a palm-like growth habit, trapping litter in the crowns of their strap-shaped leaves. Walk over to Plot 39 to see Erythrochiton brasiliensis (Rutaceae), a Neotropical understory shrub that traps litter in its crown. A short distance away, in Plot 45, a young sapling of Gustavia monocaulis (Lecythidaceae) is doing the same thing. An entirely different mode of litter-trapping is found in several genera of epiphytic orchids, including some species of Catasetum, Cymbidium, Grammatophyllum and Cyrtopodium. These orchids produce two kinds of roots: thick roots that hold the orchid to the tree on which it grows, and thin, upward-growing roots that trap litter. Cyrtopodium punctatum, an orchid native to Florida growing on several palms in the Montgomery Palmetum, readily exhibits these litter-trapping roots. The thin, wiry roots trap stray leaves and other debris and are also, presumably, able to absorb nutrients as they leech out of the trapped litter. In the wild, the private compost piles accumulated by litter-trapping plants are home to an amazing array of organisms. Ants, collembolans and mites are some of the most common occupants of litter masses, but biologists have recorded hundreds of different kinds of animals living in littertrappers. One ecologist estimated that the biomass of invertebrate species living in a forest canopy in Asia is doubled if one also counts the biomass of species living in bird’s nest ferns. Inventories of insects living in litter-trappers routinely turn up new, undescribed species, and probably many more insect species await discovery by intrepid biologists willing to dig into the private compost piles of litter-trapping plants. Litter-trapping plants are quintessentially tropical. They didn’t evolve in the temperate zone, where soils are richer and the decay process is slower. Hundreds of litter-trapping species from more than 30 families of plants are found in tropical regions of Asia, Africa and the Americas. Australia appears to be poor in litter-trappers, but this may be an artifact of under-reporting. One of the big remaining questions is: Which plants are litter-trappers? In the past, field botanists cleared away the litter before taking photographs and making specimens (no one wants to press a mound of decaying leaves infested with ants!), so litter-trapping has been under-reported in the literature. As awareness of litter-trapping plants grows—through living plant displays at Fairchild, among other means—so will our understanding of this fascinating tropical phenomenon. ABOVE A young Theophrasta jussieui just outside the Conservatory.
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