Some Very Special Brocchinia.
Brocchinia acuminata is the purely ant-fed myrmecophyte mentioned in the above list. In its cool to cold, extremely wet and immensely nutrient poor, mostly sandstone derived habitats on the high tepui plateaux, 50 % of plants were ant-inhabited.
Its form is superficially similar to that of pseudobulbous Tillandsia species but it tends to be larger in size. (Givnish et al. 1997) However, in this species, leaves are not as tightly closed above the interior hollow as they are in Tillandsia, thereby allowing some water to penetrate the interior. This is perhaps because nutrient absorption inside the tanks of Brocchinia species occurs mostly through large, living, shield cells at leaf bases. These can die if they become too dry - an important detail for cultivators to consider. However, in Tillandsia, gas intake is performed through outer layers of dead cells that incorporate vapour gaps, which help to preclude desiccation of underlying living cells. (Givnish et al. 1997.)
A further hint that this species is an ant mutualist is that it grows numerous adventitious roots between its clustered leaf bases and its trichomes are able to absorb amino acids from decomposition. Givnish et al., further postulate that this species may be able to obtain concentrated carbon dioxide (CO˛) from both ant respiration and the decomposition of their waste products as does Dischidia major. Circumstantial evidence supporting this hypothesis is that in B. acuminata, stomata are formed in sufficiently large clusters on internal leaf bases to be evident to the naked eye. Although their function is not known, they do connect to aerenchyma channels (air-filled connective tissues) that are especially large in this species. The plant’s upper photosynthetic leaf tissues sit some 30 cm (12”) away from the lower parts where ants live and exhale carbon dioxide. Perhaps the aerenchyma tubing transports concentrated CO˛ to where it is needed for photosynthesis. (Givnish et al. 1997.)
It is the most widespread of all Brocchinia species occurring in tepui scrubs, edges of bogs, and cloud forests both on the top and lower surrounds of eastern and western tepui at diverse altitudes between 600- 2100 m (1969- 6890 ft.). (Givnish et al. 1997.)
Brocchinia reducta Baker provides an unusual combination of carnivory and myrmecophytism. It is endemic to both Kukenan Tepuy, at 2200 m. (7218 ft.) and Roraima Tepuy which at 2810 m. (9219 ft.) is the highest of all tepui. This species grows on tepui sides and summits at altitudes between 900- 2200 m. (2953– 7218 ft.) where it occurs in extremely nutrient-poor, peaty to sandy soils interspersed with the competing carnivorous pitcher plant Heliamphora nutans. However, unlike B. acuminata, it has retained the use of open phytotelmata that are efficient pitfall traps for catching small invertebrates. Tightly packed yellowish, probably insect attracting leaves surround columnar liquid-impounding tanks. Outside leaf-scales are highly reflective of ultraviolet light, a well-known insect attractant and loose internal waxy scales provide no footholds for small arthropods that fall into phytotelma and drown. Impounded water in young plants emits a very distinctive smell, which is very probably an insect attractant but this smell was not observed in older plants, perhaps as we will see, a revealing observation. (Givnesh et al. 1984, Gonzales et al.1991.)
Older plants impound organic debris deposited by ants that build their nests in the dry gaps between outer leaves, using central tanks only as their refuse dumps. Thus we have a rare combination of both carnivory and myrmecophytism but this species is primarily carnivorous only when young.
Spiders frequently build webs across tank mouths therefore dropping faeces and scraps from their meals into them. (Gonzales et al. 1991.)
A lack of its own digestive enzymes has previously precluded B. reducta as being accepted as a true carnivore; however, it does release a sulphur compound (a phosphatase) into its phytotelmata that with the help of symbiotic microorganisms speeds up decomposition of trapped organics. (Plachno & Jankun 2005) Furthermore, its trichomes can absorb the bi-products of decomposition.
The only ant species recorded on the tepui studied was a Solenopsis species that was a frequently trapped victim, especially of young plants. A commensal symbiotic midge larvae Metrocnemus sp. lives in the digestive waters, as does a carnivorous Bladderwort plant Utricularia humboldtii R. H. Schomb. Interestingly, this parasite of Brocchinia tanks has the largest flowers of all Utricularia species and possibly the largest traps.
Brocchinia hechtioides Mez is not an ant-plant although outwardly it is very similar to B. reducta. The species is a fully carnivorous inhabitant of both eastern and western tepui at altitudes of 1400- 2125 m. (4593- 6972 ft.) where it grows terrestrially in nutrient-poor bogs, wet sandy savannas and on sandstone outcrops. That this plant is an accepted carnivore is probably not well known even among carnivorous plant enthusiasts. It has a more open structure than that of B. reducta with water impounded primarily in its leaf axils where it may also trap most of its prey, as does the weakly carnivorous epiphytic bromeliad Catopsis berteroniana. Growth is taller than that of B. reducta and it impounds up to 60 ml. of liquid that emits the same nectar-like scent as its better-known carnivorous congener.
Brocchinia of course require very different cultivation parameters than most if not every other bromeliad group.
An interesting YouTube introduction to the Venezuelan lost worlds can be seen at; http://www.youtube.com/watch?v=LC4W00E7jHk&feature=related
Cochliostema odoratissimum from Nicaragua, Costa Rica and Panama, is a large, very bromeliad-like phytotelm epiphyte with moderately succulent leaves that reach 1m (3.28ft.) in length. Plants attain a very large 2 m. (6.56ft.) in height, yet lovely blue flowers so typical of the Commelinaceae show that these are not bromeliads.
Paepalanthus bromelioides of the Eriocaulaceae is another little known but very bromeliad-like phytotelm that may even be fully carnivorous. It certainly catches and drowns insects between its rosetted leaves, but it may not be able to digest them, an ability considered to be an essential criterion to qualify as a fully carnivorous plant. It occurs at 1000 m. (3281 ft.) or higher altitudes on the Brazilian edge of the Gran Sabana.
Orectante sceptrum (Sometimes spelt Orechthante) of the Xyridaceae is another little known phytotelm that interestingly also occurs on the tepui of the Gran Sabana.
Collospermum hastatum the so-called Perching Lily, of the Asteliaceae family is a most unique epiphytic phytotelm that both gathers and impounds considerable quantities of rainwater in the bases of its many strongly V-shaped leaves. This robust species lives in the temperate to subtropical rainforests of New Zealand.
Cymbidium canaliculatum is an Australian orchid species that can be mentioned here because it represents yet another method of water retention for arboreal plants. It grows out of tree hollows especially in extremely hole-prone eucalypt trees where its roots penetrate deep into the soft tissues of their rotting cores. Like the previous species, it too has channelled leaves but here rainfall is directed into the plants centre hence down toward its extensive root system where it is soaked up by rotting wood masses which are further protected from the vagaries of the arid Australian climate by the trunks of home trees.
Hollow trees are actually stronger than solid trees and it is believed that internal rotting of trees is actually a well managed survival strategy permitting nutrients from within no longer important cores to be recycled into outer living tissues.
Therefore water-impounding plant species do not naturally exist in Old World rainforests; certainly no species with anywhere near the impact phytotelm bromeliads have on their local ecosystems. I add this qualifier because there are other ways in which forest plants retain water if only inadvertently such as in tree hollows, and the axis of palm and banana ‘stalks’ being obvious examples.
Now however, there are numerous bromeliad species and their hybrids distributed widely around our planet. A number of interesting questions are raised. Have any phytotelm bromeliad species established in any old world forests? If so, how are they changing local ecosystems? One would expect that evolutionary futures would be drastically changed from what they would otherwise be.
It seems that a lack of suitable pollination vectors is restricting naturalisations in at least some suitably climatic regions of our planet. Yet surely with the number of phytotelm bromeliad species/hybrids coming into contact with countless newly possible pollinators, some successful new combinations will eventually be found by Mother Nature. I see that Tillandsia ionantha, a species that hails from southern Mexico to Central America has managed to find a suitable pollinating vector in Florida but admittedly this is within connected continental landmasses where there is a better chance of having compatible pollinators.
It is a shame that human life spans are so ephemeral because future evolutionary paths will surely become ever more fascinating as humans continue to stir the ingredients of evolution in ever more fascinating ways.
These articles have grown much larger than originally envisioned yet they still remain a vastly over-simplified appraisal of the fascinations of bromeliads.
Givnish, T. Burkhardt, E. Happel, R. Weintraub, J. 1984. Carnivory in the bromeliad Brocchinia reducta, with a cost/benefit model for the general restriction of carnivorous plants to sunny, moist, nutrient-poor habitats. American Naturalist 124: 479-497.
Givnish, T. Systma, K. 1997. Molecular Evolution and Adaptive Radiation. Cambridge University Press.
Gonzalez, J. Jaffe, K. Michelangeli, F. 1991. Competition for Prey between the Carnivorous Bromeliaceae Brocchinia reducta and Sarraceniaceae Heliamphora nutans. Biotropica 23 (4B): pp602– 604.
Rowe, D. J. Ant-plants: Arboreal Wonders of Nature. A fantastic book distributed only as DVD. See; http://www.australiansucculents.com/
For pictures of Brocchinia and other genera mentioned above, click this BSI/gallery link.
An interesting YouTube introduction to the Venezuelan lost worlds can be seen at; www.youtube.com/watch?v=LC4W00E7jHk&feature=related.