Bug plants
| Bug plants | ||||||||||||
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| Systematics | ||||||||||||
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| Scientific name of the family | ||||||||||||
| Roridulaceae | ||||||||||||
| Engl. & Gilg | ||||||||||||
| Scientific name of the genus | ||||||||||||
| Roridula | ||||||||||||
| Burm.f. ex L. |
The roridula ( Roridula ), also Taupflanzen called, are the sole and only two species existing genus of the family of roridula plants (Roridulaceae) in the Capensis . The sticky leaves of the subshrubs native to South Africa catch insects that are eaten by bugs and spiders that live on the plant. Their excretions are in turn absorbed by the leaves of the plant as fertilizer.
description
Both species are evergreen subshrubs up to 2 meters high . Their roots consist of a strongly developed taproot with only weak, fine side roots . The perennial stem axis is upright, woody and only weakly branched.
In both species a clear secondary growth in thickness could be detected, in Roridula dentata also annual rings . Individual, spirally thickened tracheas are found scattered in roots and stems. In the primary trunk, the individual vascular bundles are connected to one another by a ring of fiber cells. The rays are single-row, the upright storage cells are unique . The sieve-tube plastids belong to the Ss-type (= S-type with strength).
Stems and leaves both reflect UV rays and attract insects.
leaves
The yellowish-green, linear to tapering leaves are alternate, without stipules, either with entire margins or with a short linear lobes to the side. They stand under the ends of the sprouts . The leaves are covered with stalked glands of different lengths at the leaf edges , which serve to catch insects. In contrast to that of most other carnivorous genera with sticky traps, the catching slime secreted by these glands is not based on water but on rubber and is extremely sticky. It also holds onto larger insects such as butterflies or dragonflies . What is noteworthy is the so-called circinate vernation , which is extremely rare in higher plants , in which the young leaves are rolled up like a snail during growth like a bishop's staff and unroll from the base of the leaf.
blossoms
The hermaphroditic, medium-sized and attractive flowers are in racemose , few-flowered, terminal inflorescences . The double flower envelope is not overgrown and has radial symmetry . The petals are pale purple, pink or white, broadly inverted egg-shaped and glabrous. In the bud , the petals are laid on top of each other like roof tiles ( imbricat ).
The five stamens are opposite the sepals , the thread-like stamens are not grown. The stamens start (approximately) at the base of the anthers (basifix) and have two counters . These open towards the center of the flower and are below the ovary . At the base of the anthers there is a bulge in the connective that contains nectar . The tapetum is glandular. The pollen grains all arise at the same time and are dinuclear when released. The stamens are irritable during flowering; if they are touched, the anthers at the top pop open and hurl the pollen out through the openings.
The gynoeceum consists of three intergrown carpels , the ovary formed from it is superordinate with a central angled placentation . The ovules are anatropic and have only one integument (Unitegmie). The embryo sac develops according to the polygonum type. The polar nuclei fuse before fertilization, the endosperm is cellular and the embryo develops according to the Solanaceae type. The stylus is terminal, papillose and upright.
Fruit and seeds
The fruit is a smooth, cartilaginous, triple capsule , the fruit walls tear open in the middle. It contains numerous, elliptical, dark red-brown seeds . The seeds have a diameter of 5 millimeters and have a hard seed coat with strongly thickened cell walls. Inside there is an abundant fleshy endosperm and an elongated embryo.
Cytology and Ingredients
The number of chromosomes is 2n = 12. In the epidermal cells near the side and middle ribs there are crystal sand deposits, in the endosperm and the integuments tannins . Naphthoquinones are absent, iridoids could be detected.
distribution
Bug plants are floral elements of the Capensis and endemic to the area of the former Cape Province of South Africa in the Cedar Mountains and the area around Hermanus . They grow there at altitudes between 100 and 1200 meters in mountainous, sometimes damp regions. The locations are in fynbos , a heather-like vegetation , on swampy terrain with black soils, or on slopes with seepage water or near watercourses on acidic and extremely nutrient-poor sandy soils between quartzite rocks . There the plants are associated with peat moss ( Sphagnum ) or Grubbia rosmarinifolia .
All occurrences are isolated from one another and range from a few to 2000 plants. Both species are rare and Roridula gorgonias is endangered.
ecology
Precarnivory
The bug plants use their catch indirectly in a mutualistic symbiosis with two specialized bug species of the genus Pameridea ( Pameridea marlothii and Pameridea roridulae , the latter only in Roridula gorgonias ). These live exclusively on the bug plants, find the prey animals within a few minutes of being caught and feed on the trapped animals, but in the case of insufficient prey they also suck plant sap. How exactly the bugs protect themselves from sticking has long been unclear, it has been assumed that the animals are able to hold on to the lower parts of the stalk glands of the plants through the special shape of their tarsi and are largely not in contact with them the sticky tip to come. In 2008 it could then be proven that the animals are covered all over their bodies with a thick layer of secretion that acts as an "anti-stick layer".
The plant absorbs the excretions of the bedbugs as leaf fertilizer through the cuticle and thus indirectly uses the nutrients it catches. The plants can cover up to 70% of their nitrogen requirements in this way, a very high figure compared to other carnivorous plants. Mainly caught are flying insects such as flies , wasps and other hymenoptera , up to large prey such as butterflies and dragonflies . The examination of a catch of a Roridula gorgonias revealed that it captured 109 insects larger than 2 millimeters (10.1% beetles , 80.6% two-winged ) and 112 smaller (52% fringed- winged, 35% two-winged) within eight weeks .
The crab spider Synema marlothii also feeds on the catches of the plant, but also on the bugs themselves . However, their presence harms the plants by reducing the number of bedbugs and - as a result - by reducing the nitrogen from the utilization of prey from 70% to up to 30%.
Charles Darwin first examined bug plants for a possible carnivory in 1875, but came to no conclusion. Due to the symbiosis and the lack of absorbent vessels in the glands, they were classified as a so-called precarnivorous plant based on studies by Rudolf Marloth in 1910 . It was therefore assumed that although they have devices for catching insects , they could not digest them on their own and therefore they should not be regarded as carnivorous in the true sense. In 2006, a high level of phosphatase activity was found in the epidermis , an indication that the leaf surfaces of the plants also produce enzymes and thus at least contribute to digestion, although it cannot be ruled out that these values result solely from the high metabolic activity of the plant . However, there is no doubt that the insects have the largest share in digestion.
pollination
Roridula species are mainly self-pollinating , cross-pollination is rare. The bedbugs mostly serve as pollinators. The animals pierce the connective of the anthers with their proboscis in order to get to the nectar they contain. This causes the dust bags to suddenly turn 180 degrees, release the pollen through the openings at the top of the dust bag and use it to dust the bugs.
Other animal species are also rarely used as pollinators; Allodape punctata and Xylocopa albifrons (both from the real bees family ) and Ceroctis capensis , an oil beetle, were found . The bees are so-called buzz pollinators , so the hum of the animals triggers the anthers. Visiting bees, in particular, is important for the genetic exchange of populations, as bees can also cover longer distances, but visiting the short-stalked flower, which is therefore close to the leaves, carries the risk of being caught for these animals.
Fire ecology
Both species are pyrophilic , which means they are adapted in several ways to the bush fires that occur regularly every few years and are sometimes dependent on them. On the one hand, the fires clear the vegetation and thus prevent the bug plants from being overgrown, on the other hand they allow the seeds to germinate and grow in open conditions.
Burned down older plants sprout from the refractory root stock after the fire. However, this can be delayed by the seasonal conditions, so that plants first go through the dormant phase after they have burned down and then kick out again. Up to six months can pass between fire and new growth.
Systematics
Both genus and species are clearly delineated and undisputed, two species are recognized:
- Roridula dentata L.
- Roridula gorgonias Planch.
The type species is Roridula dentata . Four other taxa described ( Roridula crinita , Roridula verticilliata , Roridula muscicarpa, Roridula × brachysepala ) are consistently discarded and classified as synonyms . The genus does not include other species described as Roridula between 1775 and 1818 , which are taxa of the - unrelated - genus Cleome in the family of the caper plants (Capparaceae).
Much less clear, however, was the position of the genre for a long time. Historically, it was assigned to the sundew plants (Droseraceae, near Bentham and Hooker 1865), the bone-leaf plants (Ochnaceae, near Planchon 1848) and the Scheineller plants (Clethraceae, near Hallier 1912). In 1924 Adolf Engler and Ernst Friedrich Gilg described the genus as an independent family, followed by Marloth (1925) and Diels (1930). Although this classification was questioned several times in the course of the 20th century, among other things by placing it among the rainbow plants (Byblidaceae), in the meantime the treatment as a separate family has established itself, and molecular genetic studies have also confirmed this. According to these, the genus is related to the American pitcher family (Sarraceniaceae) and the ray pen family (Actinidiaceae).
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Paleobotany
In 2014, two 35 to 47 million year old ( Eocene ) leaves of a Roridulaceae were described in a sample from the Russian open-cast amber mine near Jantarny . They represent the first documented fossil record of the traps of a carnivorous plant. The find confirmed the assumption already made by molecular studies that the Roridulaceae family separated from the Actinidiaceae around 38 million years ago . In addition, however, the find in Northern Europe also showed that the family was much more widespread in the Eocene than it is today, which makes the previous theories of the paleo-endite origin of the family in Gondwana seem improbable. Also with regard to the distribution areas of the related families Actinidiaceae (tropical Asia and America) and Sarraceniaceae (North and South America), a large distribution area of the family is considered probable in the light of the find. Probably only after the extinction processes after the Eocene did it become smaller, the current species in their areas of distribution would then be relics of this process.
use
The bug plants are irrelevant for humans as a useful plant. However, Marloth reports that cut branches of the plants were hung up in houses as flycatchers.
literature
- John G. Conran: Roridulaceae. In: Klaus Kubitzki (Ed.): The Families and Genera of Vascular Plants. Volume 6: Flowering plants - Dicotyledons, Celastrales, Oxalidales, Rosales, Cornales, Ericales. Springer, Berlin et al. 2004, ISBN 3-540-06512-1 , pp. 339–343.
- Wilhelm Barthlott , Stefan Porembski, Rüdiger Seine, Inge Theisen: Carnivores. Biology and culture of carnivorous plants. Ulmer, Stuttgart 2004, ISBN 3-8001-4144-2 , pp. 163-165.
Individual evidence
Most of the information in this article has been taken from the sources given under references; the following sources are also cited:
- ↑ Jeremy J. Midgley, William D. Stock: Natural Abundance of δ ¹⁵N Confirms Insectivorous Habit of Roridula gorgonias, Despite it Having No Proteolytic Enzymes. In: Annals of Botany. Vol. 82, No. 3, 1998, ISSN 0305-7364 , pp. 387-388, JSTOR 42765801 .
- ↑ Sherwin Carlquist: Wood Anatomy of Roridulaceae: Ecological and Phylogenetic Implications. In: American Journal of Botany. Vol. 63, No. 7, 1976, ISSN 0002-9122 , pp. 1003-1008, JSTOR 2441759 .
- ^ Fauna and Flora of Hermanus. Fernkloof Nature Reserve website, ( Online ( Memento of April 22, 2008 in the Internet Archive )).
- ^ A b Alan G. Ellis, Jeremy J. Midgley: A new plant-animal mutualism involving a plant with sticky leaves and a resident hemipteran insect. In: Oecologia . Vol. 106, No. 4, 1996, pp. 478-481, JSTOR 4221288 .
- ↑ Bruce Anderson, Jeremy J. Midgley: Density-dependent outcomes in a digestive mutualism between carnivorous Roridula plants and their associated hemipterans. In: Oecologia. Vol. 152, No. 1, 2007, pp. 115-120, JSTOR 40210657 .
- ^ Paul Simons: When a carnivore is not a carnivore. In: New Scientist . 2045, August 31, 1996, p. 16, ( online ).
- ^ William R. Dolling, JM Palmer: Pameridea (Hemiptera: Miridae): predaceous bugs specific to the highly viscid plant genus Roridula. In: Systematic Entomology. Vol. 16, No. 3, 1991, ISSN 0307-6970 , pp. 319-328, doi : 10.1111 / j.1365-3113.1991.tb00692.x .
- ↑ Dagmar Voigt, Stanislav Gorb : An insect trap as habitat: cohesion-failure mechanism prevents adhesion of Pameridea roridulae bugs to the sticky surface of the plant Roridula gorgonias. In: Journal of Experimental Biology . Vol. 211, No. 16, 2008, pp. 2647-2657, doi : 10.1242 / jeb.019273 .
- ↑ Bruce Anderson: Adaptations to Foliar Absorption of Faeces: a Pathway in Plant Carnivory. In: Annals of Botany. Vol. 95, No. 5, 2005, pp. 757-761, JSTOR 42796161 .
- ↑ a b Bruce Anderson, Jeremy J. Midgley: It takes two to tango but three is a tangle: mutualists and cheaters on the carnivorous plant Roridula. In: Oecologia. Vol. 132, No. 3, 2002, pp. 369-373, JSTOR 4223351 .
- ^ Charles Darwin: Insectenfressende Pflanzen (= Ch. Darwin's collected works. Vol. 8). E. Schweizerbart'sche Verlagshandlung (E. Koch), Stuttgart 1876, pp. 309-310 .
- ↑ Bartosz J. Płachno, Lubomír Adamec, Irene K. Lichtscheidl, Marianne Peroutka, Wolfram Adlassnig, Jaroslav Vrba: Fluorescence Labeling of Phosphatase Activity in Digestive Glands of Carnivorous Plants. In: Plant Biology. Vol. 8, No. 6, 2006, ISSN 1438-8677 , pp. 813-820, doi : 10.1055 / s-2006-924177 .
- ↑ a b Bruce Anderson, Jeremy J. Midgley, Barbara A. Stewart: Facilitated selfing offers reproductive assurance: a mutualism between a hemipteran and carnivorous plant. In: American Journal of Botany. Vol. 90, No. 7, 2003, pp. 1009-1015, JSTOR 4124120 .
- ^ Carnivorous Plant Database. Retrieved September 7, 2018 .
- ↑ Randall J. Bayer, Larry Hufford, Douglas E. Soltis: Phylogenetic Relationships in Sarraceniaceae Based on rbcL and ITS Sequences. In: Systematic Botany. Vol. 21, No. 2, 1996, ISSN 0363-6445 , pp. 121-134, JSTOR 2419743 .
- ^ Eva-Maria Sadowski, Leyla J. Seyfullah, Friederike Sadowski, Andreas Fleischmann, Hermann Behling, Alexander R. Schmidt: Carnivorous leaves from Baltic amber. In: Proceedings of the National Academy of Sciences . Vol. 112, No. 1, 2015, pp. 190-195, doi : 10.1073 / pnas.1414777111 .
- ^ Rudolf Marloth : Some recent Observations on the Biology of Roridula. In: Annals of Botany. Vol. 17, No. 65, 1903, pp. 151-157, JSTOR 43235665 .
