Calvaria tree

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Calvaria tree
Seeds of the calvaria tree, exhibited in the National Museum of Natural History "Naturalis" in Leiden, the Netherlands

Seeds of the calvaria tree, exhibited in the National Museum of Natural History "Naturalis" in Leiden, the Netherlands

Systematics
Nuclear eudicotyledons
Asterids
Order : Heather-like (Ericales)
Family : Sapot family (Sapotaceae)
Genre : Sideroxylon
Type : Calvaria tree
Scientific name
Sideroxylon grandiflorum
A.DC.

The sideroxylon grandiflorum ( Sideroxylon grandiflorum A.DC. ), locally called Tambalacoque, belongs to the family of sapotaceae (Sapotaceae) and comes only to Mauritius before.

description

The calvaria tree is a forest tree with a maximum height of about 20 meters. The largest measured specimens reached a diameter of 100 centimeters at chest height . The trunk grows straight, with a relatively small, compact crown, it is characterized by massive buttress roots . Younger trunks have thick, reddish tomentose hairs, older ones are bare, with a bark divided by horizontal cracks. The rather heavy wood is hard and durable and resistant to termites. It was often used as construction timber when the species was more common.

The simple leaves are heaped on the shoot tips, their leather-like, entire-margined blade is obovate to elliptical with a wedge-shaped leaf base and a slightly bent back apex, which can be indented, bluntly rounded or slightly pointed. The petiole is about 1.5 to 2 cm long, the leaf blade reaches (7-) 9 to 11 cm long and 4.5 to 6 cm wide. The upper side of the leaf is shiny, the underside with fine tomentose hairs, later balding. The spreading edge is slightly turned over and thickened. In this species the leaves of the young shoots are noticeably larger than those of older trees, they can reach three times the length of these.

The stalked flowers sit individually or in groups of two or three, directly on the wood, below the leaves, on pillow-shaped swellings between the leaf scars of the older leaves that have been shed. The sepals of the radial, five-fold flowers are about the same length as the petals . The five sepals are rounded at the apex and are leathery, thick and tomentose, with rusty hairs. The petals are fused at the base to a very short, about 1.5 mm long corolla tube, the corolla lobes are rounded and tongue-shaped. The five fertile stamens sit in front of the petals, the five sterile staminodes in the corners in between. The egg-shaped ovary has five (or six) compartments with an ovule and a simple pen .

The ripe stone fruit is about the size of a small apple, about five centimeters in diameter or slightly more. The sturdy, fleshy fruit shell is yellowish-rust-colored, smooth on the outside, the remaining remains of the calyx are in a small depression at the rounded tip. The unripe, very hard fruits become softer when ripe. Each fruit contains only one very hard, thick-skinned seed.

Distribution, habitat, ecology

The tree is endemic to the island of Mauritius. It seldom grows in the forests of the highlands, only with annual rainfall of 2500 to 5000 millimeters. The species grows extremely slowly, with an older specimen outdoors an annual growth of only 0.65 mm per year was determined. The trees are long-lived and well armed against the frequent cyclones thanks to the sturdy trunk reinforced with buttress roots .

The fruits take up to 18 months to ripen. The seeds germinate after 3 to 6 months, the germination rate in the experiment being very low, always less than 30%. Seeds that fall to the ground inside the fruit will rot without germination, so that the species is presumably dependent on fruit-eating species for reproduction, which transport and deposit the hard seed when eating the fruit.

Threat and Conservation

The calvaria tree has become extremely rare and is now threatened with extinction. The island of Mauritius has lost more than 95% of its original forest stock due to the clearing of the forests, the remaining stocks form small isolated forest fragments, almost all in the highlands. Even if the statement that only 13 overaged trees of the Calvary tree survived in 1973 turned out to be erroneous, the current population is also estimated at barely more than 500 trees (status: 1997).

The calvaria tree and the dodo

Calvary tree ( Sideroxylon grandiflorum )

Going back to an influential article by the American ecologist Stanley A. Temple , the theory has spread that the calvari tree of Mauritius would have been dependent on this presumably fruit-eating species for reproduction in co- evolution with the famous, also extinct bird dodo or dronte ( Raphus cucullatus ) now, after their extinction, also doomed to extinction. Due to the rock-hard seed coat, the seed would only have acquired the ability to germinate in the stomach of the birds with their stomach stones. To substantiate his thesis, Temple later fed fruits of the tree experimentally to turkeys ( Meleagris gallopavo ), after which their germination properties improved greatly.

The thesis was contradicted early on, but for a long time the tree species was even referred to in English as the "Dodo Tree". Because of its attractive moral quality, the thesis has found widespread use, even in school and textbooks. It could at least be confirmed that species with large fruits such as the calvaria tree have declined even more than the endangered endemic flora of the island as a whole. In addition to the dodo, other extinct fruit-eaters are now also mentioned, the disappearance of which could possibly have been the cause of the decline, such as the giant tortoises of the genus Cylindraspis. Later experiments with incised seed coats also showed that rubbing the seeds through the stomach stones of birds Germination properties not improved as expected. A connection between the decline of fruit-eating species and the decline of the tree is plausible today, but not proven, since the species is also threatened by other factors such as deforestation and introduced animal and plant species ( neobiota ). Temple's original theory is now considered unlikely.

Systematics and taxonomy

The species was first described in 1844 by the botanist Alphonse Pyrame de Candolle . Marcel Marie Maurice Dubard transferred it in 1912 to the genus Calvaria , established by Karl Friedrich von Gärtner in 1806 after a work by Philibert Commerson , which is no longer recognized today. The synonymous name Calvaria grandiflora (A. DC.) Dubard was not widely used. However, the species was misunderstood by many botanists and equated with Sideroxylon majus (CF Gaertn.) Baehni , an endemic to the island of Réunion first described in 1806 , first described under the Basionym Calvaria major C.F.Gaertn. It is therefore listed under this name in many works. John Gilbert Baker had already used the correct name in his Flora of Mauritius in 1877.

According to genetic data, Sideroxylon grandiflorum , Sideroxylon majus, and Sideroxylon sessiliflorum , another endemic species to Mauritius, are separate but closely related species that may have split off from a group of species spread across Madagascar in the Pliocene . The genus Sideroxylon also includes about 80 other species, it is mainly found in arid regions of Africa, East Asia and South and Central America.

literature

  • JG Baker : Flora of Mauritius and the Seychelles. L. Reeve & Co., London 1877, pp. 193 f., Online at biodiversitylibrary.org., Asian Educational Services, Madras / New Delhi 1999, ISBN 81-206-1427-5 (reprint).

Web links

Commons : Calvaria tree ( Sideroxylon grandiflorum )  - Collection of images, videos and audio files

Individual evidence

  1. ↑ Arthur W. Hill: The Genus Calvaria, with an Account of the Stony Endocarp and Germination of the Seed and Description of a New Species. In: Annals of Botany. New Series 5 (20), 1941, 587-606, JSTOR 42906846 .
  2. ↑ a b J. G. Baker: Flora of Mauritius and the Seychelles.
  3. ↑ a b c Claudia Baider & FB Vincent Florens: Current Decline of the "Dodo Tree": a case of broken down interactions with extinct species or the result of new interactions with alien invaders? Chapter 11 in: William F. Laurance & Carlos A. Peres (editors): Emerging Threats to Tropical Forests. University of Chicago Press, Chicago and London, 2006, ISBN 978-0-226-47021-4 .
  4. ↑ Peter S. Wyse Jackson, Quentin CB Cronk, John AN Parnell: Notes on the regeneration of two rare Mauritian endemic trees. In: Tropical Ecology. 29, 1988, 98-106.
  5. ^ List of Indigenous Plants. The Forestry Service Under the aegis of the Ministry of Agro Industry and Food Security, Republic of Mauritius. Retrieved February 26, 2019.
  6. ^ A b S. A. Temple: Plant-animal mutualism: coevolution with Dodo leads to near extinction of plant. In: Science. 187, 1977, 885-886.
  7. ↑ Owadally, AW 1979. The dodo and the tambalacoque tree. In Science. 1363-1364. doi: 10.1126 / science.203.4387.1363
  8. ^ Paul M. Catling: Extinction and the importance of history and dependence in conservation. In: Biodiversity. 2 (3), 2011, 2-14. doi: 10.1080 / 14888386.2001.9712550 .
  9. ↑ David Quammen , 2001. The Song of the Dodo. A journey through the evolution of the island worlds. Ullstein, Munich, ISBN 3-548-60040-9 .
  10. ↑ Malika Virah-Sawmy, John Mauremootoo, Doreen Marie, Saoud Motala, Jean-Claude Sevathian: Rapid degradation of a Mauritian rainforest following 60 years of plant invasion. In: Oryx. 43 (4), 2009, 599-607. Full text at Cambridge Core
  11. ↑ John B. Iverson: Tortoises, Not Dodos, and the Tambalacoque Tree. In: Journal of Herpetology. 21 (3), 1987, 229-230.
  12. ↑ The Widespread Misconception that the Tambalacoque or Calvaria Tree Absolutely Required the Dodo Bird for its Seeds to Germinate. In: Plant Science Bulletin. 50 (4), 2004.
  13. ↑ archive.org .
  14. ↑ Gail Stride, Stephan Nylinder, Ulf Swenson: Revisiting the biogeography of Sideroxylon (Sapotaceae) and an evaluation of the taxonomic status of Argania and Spiniluma. In: Australian Systematic Botany. 27, 2014, 104-118. doi: 10.1071 / SB14010