Spike trisetum  (Trisetum spicatum)

The spike trisetum has yet to be classified by the IUCN.

A tufted perennial plant with tall, upright stems (2) (3) (4), the spike trisetum (Trisetum spicatum) is a rather widespread yet little-studied species (4). The spike trisetum’s alternative common name, ‘downy oat-grass’, refers to the characteristic velvety hairs found on the stem and the flowering spike (4). On the stem, these hairs are typically fine, soft, short and sometimes matted (3), and are often curved forwards and upwards (2). The hairs are usually densest below the flowering spike, which is a loose, branching cluster of flowers, known as the ‘panicle’ (2) (3).

The panicle of the spike trisetum is short, dense and usually pale purplish-pink (4) (5) (6), although it may also appear gold-purplish to brown-purple (2). The branches of the panicle are short, and each spike contains two or three individual florets (tiny, individual flowers) (3) (6). The glumes, which are membranous bracts surrounding the spike, are usually shorter than the florets and are often unequal in size (2) (3) (5). 

The lower bracts or flowering scales of the florets, known as ‘lemmas’, have a long, stiff bristle, called an ‘awn’, on the upper side, which is often bent and twisted. The lemmas are usually smooth, but curve and become rougher and more purplish towards the base (2) (4) (6).

The leaf blades of the spike trisetum are usually flat or rolled. They are either smooth or covered in very soft, fine hairs (2) (3), and the margins of the leaves are often bristly (3). The leaf sheaths of this species are also covered in fine, velvety or downy hairs (2) (3) (5).

The appearance of the spike trisetum varies greatly across its range. As a result, this species is often separated into numerous different subspecies and varieties, which has resulted in an extremely confusing taxonomy (2) (3) (7) (8).

Subspecies of spike trisetum are distributed worldwide, being found throughout Europe, Asia, Australia and New Zealand, and North, Central and South America (2) (3).

In North America, the spike trisetum occurs in Greenland, and from Labrador to British Colombia in Canada. In the United States, the spike trisetum occurs from Alaska, south to New Hampshire, Vermont, Connecticut, Pennsylvania and North Carolina in the east, centrally in the Great Lakes states of Michigan, Wisconsin and Minnesota, and south as far as Colorado and California in the west (2) (4) (6) (7).  

The spike trisetum occurs primarily in open, relatively exposed habitats, such as heathland, rocky outcrops and ridges. It is also found in open woodland and subalpine and alpine meadows (3) (8), as well as in boreal forest and on exposed lake shores (8). This species is most common in rocky and gravelly areas (7), and in North America it is usually found on rock ledges and in crevices (4) (8).

Relatively few studies have looked at the biology of this species (4). The spike trisetum is a member of the Poaceae, or grass family (4). In Wisconsin in the United States, the spike trisetum blooms in June, with fruiting generally occurring in July. However, it is a widespread species, hence the timing of flowering and fruiting is likely to vary greatly depending on location (9).

The seeds of the spike trisetum are unusual in having a liquid endosperm (the part of a seed that acts as a food store for the developing plant). Unlike in most other plants, the liquid endosperm of the spike trisetum remains even after the seed has matured. The wall of the seed remains leathery, and there are usually very small gas bubbles trapped in the liquid inside (10). 

The spike trisetum is threatened by the unregulated development and excessive use of shoreline habitats around Lake Superior in the United States (4).

Elsewhere across its range, the spike trisetum is likely to be similarly threatened by recreational activities and habitat loss associated with increasing development (4).

A relatively rare species, the spike trisetum is considered ‘Threatened’ in Wisconsin (9) and of ‘State Special Concern’ in Michigan in the United States (4).

At present, there are no known conservation measures in place for the spike trisetum. Around Lake Superior, this species would benefit from the protection of its shoreline habitat (4).

Further studies into the natural history of the spike trisetum would greatly benefit future conservation and management plans. Recommended areas of study include research on seed dispersal, as well as on this species’ genetic diversity (4).

Find out more about the spike trisetum:

• Michigan Natural Features Inventory - Spike trisetum:
  http://web4.msue.msu.edu/mnfi/abstracts/botany/Trisetum_spicatum.pdf