Oreobolus

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Oreobolus

Description

Dwarf glabrous perennials, forming very dense cushion-like tufts. Leaves equitant, usually exactly distichous, sometimes less regularly imbricate, rigid, narrow, canaliculate, obtusish, dark-coloured at the top; Inflorescence racemose (consisting of a few axillary, solitary or binate peduncles each bearing a single spikelet), almost capitate, or reduced to a single terminal spikelet. Flower pseudoterminal (see notes). Stamens 3;

Distribution

Asia-Tropical: Australasia:, Tasmania (Tasmania present) Chile: present Hawaiian Islands: present New Zealand: present Southern America:, Ecuador (Ecuador present); Venezuela (Venezuela present) Tahiti: present present
The number of species (about 8) is not unanimously agreed on; O. obtusangulus GAUD, in Chile, O. goeppingeri SUESSENG. (not seen) in Central America, O. venezuelensis STEYERM. (not seen) in Venezuela and Ecuador, O. furcatus H. MANN in the Hawaiian Islands, the remaining ones in Tahiti, New Zealand, Australia (and Tasmania), and Malesia. Of the 3 Malesian spp. 2 are endemic. See distribution maps in and (in which Tahiti is omitted). .

Ecology

Microtherm genus, in the tropics only on the high, ancient mountains, in swampy or rocky localities; in New Zealand descending to sea-level.
The species of Oreobolus form pin-cushions to dense tufts which may extend and merge into large cushions. When the tufts are separate the central part dies off, remains sterile and represents a hole, and this remarkable formation of ‘fairy rings’ is found in Malesian high mountains in several other pin-cushion plants (Monostachya, Centrolepis, Eriocaulon). See , and .
Oreobolus is in Malesia nearly always found associated with the grass Monostachya, and with Centrolepis, Gaimardia, and Eriocaulon, which are all of similar life form.

Notes

The species of Oreobolus are similar in habit to and not rarely confused with some Centrolepidaceae (Gaimardia) and Juncaceae (Distichia). The hypogynous scales closely resemble the perianth segments in Juncaceae and Restionaceae. However, because of the structure of the spikelet and the single, basal, anatropous ovule Oreobolus must certainly be included in Cyperaceae.
According to PFEIFFER and KÜKENTHAL the stamens are placed in 2 series, one belonging to the outer series, two to the inner one. This statement is obviously based on the diagram of the flower in . In my opinion this diagram is wrong, as I always find the stamens opposite the outer perianth segments, consequently all belonging to a single (viz the outer) series, in agreement with .
The flower in Oreobolus is generally considered terminal, i.e. placed on the top of the rachilla. However, as next to the flower there is a minute rachilla internode bearing a vestigial glume, the internode bearing the flower is the penultimate one.
KÜKENTHAL () subdivided the genus into 2 sections:
Sect. Squamellati. Perigone consisting of 6 flat scales persistent on the rachilla when the fruit has fallen off. Style-base hardly incrassate, caducous. Nut 1-1½ mm long, truncate at the apex.
Sect. Setiferi. Perigone consisting of 6 whitish bristles apparently not persistent on the rachilla. Nut 2½ mm long, at the top contracted into the style-base.
To sect. Setiferi belongs only O. ambiguus, according to KÜKENTHAL in many respects a transition to Schoenus (hence the specific epithet). I find the hypogynous scales in this species persistent on the rachilla and, though very narrow, flat and similar in shape to those of O. kϋkenthalii. In sect. Squamellati the fruits are not always truncate, and in O. kϋkenthalii and O. furcatus up to 2 mm long. I do not see any reason for placing O. ambiguus in a separate section.

Citation

PFEIFF. - in Fedde, Rep. 23. 1927: 339, 350
BOECK. - in Linnaea. 1874: 230
KÜK. - in Fedde, Rep. 48. 1940: 60