Oreostylidium subulatum

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Oreostylidium subulatum
Systematics
Asterids
Euasterids II
Order : Astern-like (Asterales)
Family : Stylidiaceae
Genre : Oreostylidium
Type : Oreostylidium subulatum
Scientific name of the  genus
Oreostylidium
Berggr.
Scientific name of the  species
Oreostylidium subulatum
Berggr.

Oreostylidium subulatum is the only species of the monotypical genus Oreostylidium within the Stylidiaceae . It is endemic to New Zealand .

Oreostylidium subulatum is a very small plant with rather inconspicuous and small, white flowers. Below the flower, the plant has trichomes , which are structured in the same way as in the closely related species of the genus Stylidium and enable them to live in a carnivorous way . Oreostylidium subulatum is not considered a carnivorous species, but there have not yet been any relevant studies as to whether it produces digestive enzymes and whether it could be carnivorous.

features

Oreostylidium subulatum is a very small plant with a height of about two to three centimeters. The sessile leaves are linear to awl in shape. They reach a length of 10 to 40 mm and a width of 1 to 2 mm and are in a dense, basal leaf rosette . The leaves are also hairless, soft and entire, rarely pinnate at the tip. The stomata have no daughter cells (anomocytic), as is the case with Donatia, for example . The simply structured and unbranched root has a central cylinder with four xylempoles ( tetrarch root ). The plants form stolons or rhizomes up to 6 cm in length, these are divided by internodes .

The very short flower stem, which does not protrude from the rosette of leaves, is thin and upright. It has a maximum height of two to three centimeters and is occupied by glandular trichomes , which correspond to those of the shot plants and enable them to live a carnivorous way of life through the digestive enzymes they contain . Bracts are sometimes present, but often not, when they are very small and linear.

The inflorescence consists of a single, radially symmetrical white flower . The petals sit evenly on the flower and are the same in shape and size, the flower veining is simple and only slightly branched. The calyx is upright and compressed, and it is almost as wide as the ovary . It consists of five intergrown leaves. The structure of the five petals corresponds to the flowers of the Forstera and Phyllachne species of New Zealand, which are also classified in the Stylidiaceae .

Like the shot plants, Oreostylidium has a column in which the two stamens are fused with the ovary , which consists of two carpels . The ovary is large, cylindrical, and elongated. It is narrowed at the connection to the flower stem. However, unlike the shot plants, the column is immobile and does not react to touch.

After flowering, a 5 to 8 mm long, 4 to 5 mm diameter, broadly oval to inverted ovoid capsule fruit forms .

The chromosome set ( karyotype ) of Oreostylidium subulatum consists of 2n = 30 chromosomes.

distribution and habitat

Mount Ruapehu on the North Island of New Zealand

Oreostylidium subulatum is endemic to New Zealand , but the species is not as locally restricted as the other species of the Stylidiaceae, members of the genera Forstera and Phyllachne . According to a report by R. Good in 1925, the species is restricted to the South Island of New Zealand, but according to earlier reports it was also found in the Ruapehu area on the North Island . On the South Island, occurrences on Swampy Hill near Dunedin and the Grampians near Nelson have been described.

In their habitat, Oreostylidium subulatum, like the species of Forstera and Phyllachne, is restricted to the montane and subalpine altitudes. The species is classified as not endangered in New Zealand.

Until a few years ago there were very different opinions about the colonization of New Zealand by Oreostylidium subulatum and the other species of the Stylidiaceae. In 1968, Wardle assumed that the ancestors of these species, as evolutionarily very old genera, had already lived in Antarctica and should have reached New Zealand via Tasmania . The ancestors are said to have survived on depleted soils at high altitudes before they developed into montane species in the Pliocene . Raven 1973 consider that it was likely that the montane species only during by the collision of the Australian plate with the Eurasian plate outgoing orogeny in the Pleistocene were drifted or late Pliocene through Australia to New Zealand and have established themselves in the newly created habitats. Based on the molecular biological results of the relationship analysis of Oreostylidium subulatum and the shot plants ( Stylidium ) native to Australia , it is assumed that the species originated around three million years ago and that the parent species drifted from the Australian mainland.

History of Science and Systematics

Discovery and Classification

The first description of Oreostylidium subulatum was made in 1864 by William Jackson Hooker as Stylidium subulatum in the genus Stylidium . The classification was made on the basis of individuals without flowers and he related the classification to the morphology of the fruit as well as to the similarities of the ecological demands on the habitat . Within the genus he placed the species in the subgenus Tolypangium due to the fruit morphology . In 1878 Ferdinand von Mueller placed Stylidium subulatum in the related genus Phyllachne due to the flower morphology and in the same year Sven Berggren placed it as the only species in the monotypical genus Oreostylidium which he had newly described .

In 1887, William Colenso described a second species of the genus and named it Oreostylidium affine based on morphological differences with previous descriptions of Oreostylidium subulatum . During the description, he already stated that he was not entirely sure about the new species, but that the specimens available to him differed from the descriptions by Berggren and Hooker. O. affine was later included as a synonym for Oreostylidium subulatum .

The current discussion about the flower morphology as well as the molecular biological results suggest a new classification in the genus Stylidium , where the species should be included as a sister species of Stylidium graminifolium . Accordingly, it is likely that Oreostylidium subulatum will be listed again under its first name Stylidium subulatum from 1864 with the next revision of the Stylidiaceae .

Oreostylidium and Stylidium

Due to the similarities in flower structure, it was proposed to include Oreostylidium subulatum in the genus Stylidium , but this was discarded due to the clear differences. According to some researchers, Oreostylidium subulatum should represent an extreme form of the so-called pedomorphosis , i.e. the flower structure should be derived from a very early stage of flower development to complete Stylidium flower. Alternatively, it is considered whether the flowering could be a result of reduction . This process is said to have taken place through the isolation of the species on New Zealand. The entire population of Oreostylidium subulatum can therefore be traced back to a very small founder population , in extreme cases even to a single seed that was drifted from Australia to New Zealand. Due to the new habitat and, above all, the lack of the pollinator species typical of Australia , for which the highly specialized flowers of the Stylidium species are designed, a complete change in flower morphology took place in the founder population towards non-specifically pollinable flowers. Unlike the flowers of the Stylidium species, these flowers allow an obligatory self-fertilization .

Inflorescence of Stylidium graminifolium . Show molecular data that S. graminifolium probably the sister species of subulatum Oreostylidium is

These considerations are supported by molecular biological studies that identify Oreostylidium subulatum as a sister species of Stylidium graminifolium . On the basis of different genes of the chloroplasts - DNA , rbcL and ndhF , it was found in 1998 that Oreostylidium subulatum was classified within the Stylidium species in all of the resulting family trees . In 2002, a close relationship between Stylidium graminifolium and Oreostylidium subulatum was found, which could be identified as sister species within the genus Stylidium . Based on the genetic difference between the two species, it was calculated that the species split from a common parent species , which anatomically corresponds to Stylidium graminifolium , into two species should have occurred about three million years ago. Based on these results, a return of Oreostylidium subulatum to the genus Stylidium was requested.

supporting documents

  1. ↑ a b L. J. Rapson: Vegetative Anatomy in Donatia, Phyllachne, Forstera and Oreostylidium and its Taxonomic Significance. In: Transactions and Proceedings of the Royal Society of New Zealand 80, 1952: Pages 399-402 ( full text )
  2. ↑ DW Darnowski, DM Carroll, B. Płachno, E. Kabanoff, E. Cinnamon: Evidence of Protocarnivory in trigger Plants (Stylidium spp .; Stylidiaceae) Plant Biology 8, 2006; Pages 805-812, doi : 10.1055 / s-2006-924472 .
  3. ↑ Douglas Darnowski, Stephen Moberly, Bartosz Plachno: Triggerplants (Stylidium spp .; Stylidiaceae): A Previously Unrecognized Genus of Carnivorous Plants. , Presentation Botany & Plant Biology 2007 , 7. – 11. July 2007, Chicago, Illinois, Session Cp52, Number Cp52001, Abstract ID 18, ( Abstract )
  4. ^ YES ways: Corolla venation in Stylidiaceae. in Journal of the Royal Society of Western Australia 84, 2001; Pages 97–101 ( PDF ( Memento of September 29, 2007 in the Internet Archive ))
  5. ↑ a b c Colenso, W. (1887). Art. XXVII. — On new Phœnogamic Plants of New Zealand . Read before the Hawke's Bay Philosophical Institute, September 12, 1887. Transactions and Proceedings of the Royal Society of New Zealand , 20: 197.
  6. ↑ a b Factsheet ( memento of October 4, 2007 in the Internet Archive ) of the plant in the New Zealand Plant Conservation Network
  7. ^ R. Good: On the geographical distribution of the Stylidiaceae. in New Phytologist 24 (4), (1925): pp. 225-240.
  8. ↑ a b c d e f S.J. Wagstaff, J. Weg: Patterns of diversification in New Zealand Stylidiaceae in American Journal of Botany , 89 (5), 2002: pages 865-874. ( Full text )
  9. ↑ a b Buchanan, J. (1879). Art. LVI. — Notes on New Zealand Plants . Read before the Wellington Philosophical Society, February 21, 1880. Transactions and Proceedings of the Royal Society of New Zealand , 12: 380.
  10. ↑ a b c N. Laurent, B. Bremer, K. Bremer: Phylogeny and generic interrelationships of the Stylidiaceae (Asterales), with a possible extreme case of floral paedomorphosis. in Systematic Botany , 23 (3), 1999: pages 289-304.

Web links

This version was added to the list of articles worth reading on July 15, 2007 .