Besides the common carnivorous plants, there are many obscure carnivorous plants. Those under-discovered carnivorous plants are considered as protocarnivorous plants and sometimes referred to as paracarnivorous, subcarnivorous or borderline carnivores plants. Plant in this category is slightly different from carnivorous plants. Protocarnivorous plants can trap and kill insects or other small animals. But they do not digest the prey and absorb the nutrients from the victims due to the absence of digestive enzymes in the juices. Although there are some carnivorous plants that obtain the nutrients through mutualism symbiosis such as bacteria to produce the enzymes, they are generally referred to as carnivores as they gain some benefits such as nutrients from it.
In Australia, there are two species of carnivorous plants which related to Utricularia under the family of Lentibulariaceae. They are a subgenus of Utricularia, Polypompholyx multifida which commonly known as pink petticoat and Polypompholyx tenella which referred to as pink fans. Both species under the genus Polypompholyx are native to West Australia. These two species both have narrow, oblong, and green leaves that form a rosette encircling the base of the scape. P. multifida has the leaves seldom exceeding two inches while P. tenella has the leaves that are not more than half an inch. These two species both bloom pink flowers with yellow palates per scape (leafless flower stalk) with the length of the scape up to twelve and three inches for P. miltiflora and P. tenella respectively. There is a white flower variant for P. multifida. They are generally similar to Utricularia but their trap is slightly different from that of Utricularia. The trap of Polypompholyx has the entrance located on the same side of the trap as its footstalk (attachment) to the stem. Whereas, the trap of Utricularia is attached to the stem at the end of the trap that is opposite from the trap entrance. The overall structure of the trap of Polypompholyx is similar to a handheld palm-upwards with the fingers bent toward the wrist that used the same mechanism as Utricularia which is suction to catch the prey like tiny insects as the terrestrial Utricularia.
There are two carnivorous bromeliads. Brocchinia reducta and Catopsis berteroniana. Bromeliad is a monocot flowering plant from the family of Bromeliaceae. Brocchinia reducta commonly known as brocchinia that is originated from south of the Orinoco River, Gran Sabana, and found in the Guayana Highlands. In addition, Catopsis berteroniana often called powdery strap air plant or powdery catopsis which is native from Southern Florida to Southern Brazil. Both Brocchinia reducta and Captosis berteroniana are epiphytic species that perch on trees and shrubs as well as on the substrates that are containing low mineral nutrient contents. Both can be propagated through the separation of the crowns. The hypothesis of the carnivory property of the bromeliads is because of the impounded water in between the leaves or overlapping leaf bases that share a similar characteristic to the pitchers. Small insects and animals can blunder and drown. Both Brocchinia reducta and Captosis berteroniana share the adaptation for carnivory by having steeply inclined leaves that coated with wax that prevent the escape of insects.
Apart from the waxy surface of the inner leaves, they also have bright color leaves, which are yellow-green leaves that held nearly vertically that may aid in the attraction of the prey. The typical victims are small insects such as ants and other arthropods like pseudoscorpions, spiders, mites, chironomid, and mosquito larvae. The nectary solution is found from the “tank” fluid which is believed to attract small insects. The “tank” is referred to as the pools of water which scientifically known as phytotelmata. Scientists had found that the trichomes of the Brocchinia reducta and Catopsis berteronian are unusual in terms of the morphology and function. They had studied that the trichomes may be specialized in absorbing leaf hairs to absorb the amino acid from the breakdown of the bodies at a high rate. Although both Brocchinia reducta and Catopsis berteroniana are the least specialized of the known carnivorous plants due to the absence of the recognizable digestive glands and specialized nectar glands in the pitfall mechanism, it does fulfill the requirement of being a carnivorous plant.
Genlisea sp. which commonly known as the corkscrew plant under the family of Lentibulariaceae, which grows in tropical Africa, Madagascar, and South America in damp to wet substrate. It prefers waterlogged conditions which often found along with Utricularia and Drosera. It can be propagated through leaf pulling quickly. Similar to Polypompholyx, Genlisea is closely related to Utricularia but the traps are distinctive from that of Utricularia. It is rootless herbaceous perennials or annuals carnivorous plants that have two forms of leaves that arise from the slender rhizome, mainly linear or oblong leaves which grow upward and leaves that modified into traps, known as forked trap. It has leafless flower stalk which can up to sixteen inches that bear several flowers which can be shades of blue, purple, violet, white, or yellow that structurally similar to the flower of Utricularia. Its trapping leaves are the traps consist of a footstalk that attached to the rhizome with the bulb-like bladder. It is hanging downward in the water with a hollow tube connects to the bulb cavity terminate with an opening. Its trapping mechanism is similar to a maze in which it has numerous separated trap entrances at each twist in which the fine hairs will direct the prey toward the bulb that processes the prey (tiny aquatic insects) through digestion.
There is an utterly strange genus which is Philcoxia, under the family of Plantaginaceae. Under this genus, Philcoxia bahiensis, Philcoxia goiasensis, and Philcoxia minensis. There are very few studies on these plants as it is still not clear whether they are a perennial or annual plant. The plants grow in a near-desert condition which is extremely hot during the daytime and cool at night with very little rain. The substrate is relatively simple which is pure white quartz sand and grows at a high light intensity. Philcoxia has a small swollen stem or taproot with disk-shaped minute leaves-like structures found at the end of a filament-like stalk. Their real leaves are underground which are located just below the sand surface. The leaves-like arrangements are their specialized leaves which have very tiny glands that secrete mucilage that similar to that of butterwort leaves. Their targeted prey are appeared to be nearly microscopic nematodes. The species of Philcoxia can be differentiated with the pretty flowers which can be pink or purple that connected with zigzagging stalks that are about eight inches long.
There is a microscopic carnivore that is under-discovered as most people never see and few know the existence of this genus, Dactylla. However, it is classified as a mold which is not a plant. These under-discovered species are less popular because of the difficulty to cultivate in lab or greenhouse conditions. Nevertheless, there are some collectors who have paid attention to these under-discovered species and thus rising the trends of cultivating these species. Some of those are nematophagous fungi who are able to trap and kill parasitic nematodes, thus has vast potential in agricultural and horticultural practice to target parasitic nematodes.
Frank, J. H., & O’meara, G. F. (1984). The bromeliad Catopsis berteroniana traps terrestrial arthropods but harbors Wyeomyia larvae (Diptera: Culicidae). Florida Entomologist, 418-424.
Givnish, T. J., Burkhardt, E. L., Happel, R. E., & Weintraub, J. D. (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. The American Naturalist, 124(4), 479-497.
Swenson, A. A. (1977). Cultivating carnivorous plants. Doubleday.
Pietropaolo, J., Pietropaolo, P. A., & James. Pietropaolo. (1999). Carnivorous plants of the world. Timber Press.
D’amato, P. (2013). The savage garden, revised: Cultivating carnivorous plants. Ten Speed Press.