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Oreostylidium
''Oreostylidium'' is a genus of flowering plants in the family Stylidiaceae with a single species, ''Oreostylidium subulatum'', that is endemic to New Zealand. ''O. subulatum'' is a very small plant with small, white flowers. It has a complicated botanical history that has led to a few proposals to move ''Oreostylidium'' to the related genus ''Stylidium''. The researchers cite molecular data and suspect that this species is an extreme example of floral paedomorphosis. This would not be an unprecedented move since the single species was initially described as ''Stylidium subulatum'' in 1864 and later moved to its own genus by Sven Berggren in 1878. It possesses the same kind of glandular trichomes underneath the flower that make ''Stylidium'' species carnivorous plants, but it has not yet been tested for the presence of digestive enzymes.
== Characteristics ==
''O. subulatum'' is a very small, cæspitose, and densely tufted plant about 2-3 cm tall. The 2 cm long linear-subulate leaves form a basal rosette close to the ground. The leaves are glabrous with entire margins. The scape, arising from the rosette of leaves, is slender, erect, and about 2 cm tall. The scape, like most species in the related genus ''Stylidium'' is covered with glandular trichomes. Each scape produces a single flower. The calyx is erect, stout, and very broad (nearly as broad as the ovary). The ovary is large, oblong, sub-cylindrical, tapering and jointed on to scape.〔Colenso, W. (1887). (Art. XXVII.—On new Phœnogamic Plants of New Zealand ). Read before the Hawke's Bay Philosophical Institute, 12 September 1887. ''Transactions and Proceedings of the Royal Society of New Zealand'', 20: 197.〕
The flower corolla consists of solitary actinomorphic, white flowers with five petals that most resemble the flowers of ''Forstera'' and ''Phyllachne'' (both also in Stylidiaceae). Like all ''Stylidium'' species, ''O. subulatum'' also possesses a column, which is the fused stamens and stigma. But unlike ''Stylidium'' species, it is insensitive or non-mobile and does not move in response to physical stimuli. It has been suggested that ''Oreostylidium'' be merged into the genus ''Stylidium'', but the morphological characteristics of the two genera are dissimilar. Researchers have suggested that the floral form ''O. subulatum'' had developed by an extreme example of paedomorphosis or reduction. This process may have begun as a result of ''O. subulatum'''s isolation on the islands of New Zealand. Researchers believe that this species has its origins in Australia and was established in New Zealand by a very small population and perhaps from a single seed. Faced with survival in a new environment and possessing a flower designed for specific Australian pollinators, the species underwent rapid changes to its morphology. The hypothesis presented in these studies suggests this is how ''O. subulatum'' evolved from a common ancestry lineage with ''Stylidium graminifolium'' into the pollinator-generalist it is today. There is also a shift from the ''Stylidium''-like flower designed for cross-pollination to obligate autogamous pollination. This allowed the plant to perform sexual reproduction in its morphologically immature state because the complicated ''Stylidium''-like flowers were not required for pollination.〔Laurent, N., Bremer, B., and Bremer, K. (1999). Phylogeny and generic interrelationships of the Stylidiaceae (Asterales), with a possible extreme case of floral paedomorphosis. ''Systematic Botany'', 23(3): 289-304.〕〔Wagstaff, S.J. and Wege, J. (2002). (Patterns of diversification in New Zealand Stylidiaceae ). ''American Journal of Botany'', 89(5): 865-874.〕
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