- Scientific name: Aristida purpurascens Poir.
- Species of Greatest Conservation Need (MA State Wildlife Action Plan)
- Threatened (MA Endangered Species Act)
Description
Purple needlegrass flowers. Photo credit: Margaret Curtin
Purple needlegrass (Aristida purpurascens) is a rare, densely tufted perennial belonging to a distinctive genus of mostly xerophytic (drought-adapted) grasses which are easily recognized by their long-awned "bottlebrush" flower spikes. Purple needlegrass has smooth, upright stems from 30-75 cm (1 to 1.5 ft) high which branch from the lower nodes of a hard, closely sheathed base. The narrow leaf blades (<0.2 mm; <1/8 in) are flat and smooth below, but slightly hairy with rolled-in margins above. As the leaves mature, they become curled and slacker. The flowers first appear in a dense, narrow, dark purple-brown panicle whose length is as much as 1/3 to 1/2 the height of the plant. Each flower of the inflorescence is borne in a single, 7-10 mm (0.3-0.4 in) long, pointed spikelet which consists of several narrow, overlapping chaffy bracts (modified floral parts) with three conspicuous awns (hairlike bristles) projecting from one of the inner bracts. In purple needlegrass, all three awns are straight, erect, and about equal in length (1.5-3 cm; 0.6-1.2 in). As the inflorescence matures from mid-August on, the awns spread open so that they are widely and equally separated from each other and horizontal to the axis of the flower spike. Once mature, the inflorescence loses its purple coloration and turns a pale straw color.
In most cases, species of Aristida may be distinguished by differences in the general arrangement or shape of the inflorescence. Aristida species are distinguished from other grasses by their narrow 1-flowered spikelets with three awns. The awns are bent and twisted in distinctive ways. For the species to be positively identified, comparison of the relative length and divergence of the fully developed awns on mature plants is required. Barrens needle-grass (Aristida longespica) is an annual with smaller and narrower flower spikes, having flowers with two erect lateral awns that are shorter than the horizontally positioned middle awn. It also tends to grow in seasonally moist habitats. Prairie needle-grass (A.oligantha) is a soft-based perennial and introduced roadside weed with a fewer-flowered panicle and spikelets with three equal, but much longer (3.5-7 cm; 1.4-3.9 in) divergent awns. Seabeach needle-grass (A. tuberculosa, Threatened) is a rare coastal dune annual which can sometimes occur inland on sandy scrapes. These "bottlebrush" flower panicles are shorter, more open, and wider due to long (3-5 cm; 1.2-2 in), widely spreading awns which are also spirally twisted at their base.
Life cycle and behavior
Although growing and producing leaves much earlier in the season, this species does not produce mature flowers and seed until late August into October. The mature florets with dry awns are needed to identify this grass to species. Like most grasses, it is wind pollinated. Once the seeds are mature, in dry conditions, the awns spread wider and are more easily pulled off into the fur of passing animals. Once the seeds fall off of the passing animal into the soil, the awns may work to push the seeds deeper into the soil with alternating damper and drier weather cycles.
Population status
Close up of purple needlegrass. Photo credit: Kelly Omand, Nantucket Conservation Foundation
Purple needlegrass is listed as Threatened in Massachusetts because of the widespread succession of grasslands and open fields to forests. This species clearly prefers frequent disturbance and shows intolerance of shade or competition from encroaching woody plants. Changes in human land use practices have had a major part in changing the amount of open land available for this species to grow. In the past, grazing, agriculture, and fire maintained abundant open suitable habitat. Since 1999, populations of purple needlegrass remain in only ten towns, in Dukes, Nantucket, Plymouth, Bristol and Essex Counties, occurring mostly in small remnant patches of habitat. It is known to have occurred in Middlesex County from historical herbarium records, as well as in Hampden county. Out of the 24 known occurrences, only 9 are doing well. There are an additional 42 populations that have not been observed since 1999.
Distribution
Purple needlegrass is found in a variety of open, sandy habitats, including prairies, which contributes to its wide distribution throughout eastern North America from Massachusetts to Florida and Texas, and inland and north to Michigan, Wisconsin, southern Ontario and eastern Nebraska. It is considered rare in several states, mostly on the edges of its range, including Massachusetts, Connecticut, Rhode Island, Florida, Nebraska, New York, Ohio, Pennsylvania and West Virginia. It is also considered rare in Ontario.
Distribution in Massachusetts
1999-2024
Based on records in the Natural Heritage Database
Habitat
Purple needlegrass is usually found in the dry, nutrient-poor, sandy habitats known as heathlands and sandplain grasslands. These rare and local plant communities are scattered along the New England coastline, persisting where human land use practices and natural stresses from salt spray, fire and storms inhibit the growth of woody shrubs and trees. Purple needlegrass can also grow in maintained or disturbed areas such as grazed pastures, fire lanes, rough areas on golf courses, and powerline openings when trees are excluded. Sandplain grasslands are dominated by ubiquitous prairie bunch grasses like little bluestem, big bluestem, poverty grass, redtop, and indian grass. Also characteristic of and often restricted to grasslands are low, broadleaved herbs such as bush-clovers, asters, golden heather and bushy rockrose. Grassy heathlands are highly stressed, xeric, sparsely vegetated, low shrub communities found on sandy coastal headlands and in openings in pitch pine-scrub oak barrens. Inhospitable to most plants, these areas are successfully vegetated by large patches of bayberry, huckleberry, golden aster, and hardy grass species. Clarke and Patterson (2007) found that a handful of species were positively associated with a larger population of purple needlegrass within Manuel F. Correllus State Forest, included Hypericum gentianoides, Polygonella articulata, Pityopsis falcata and Viola pedata.
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Typical purple needlegrass habitat. Photo credit: Kelly Omand, Nantucket Conservation Foundation
Threats
Massachusetts currently represents the northeastern extent of purple needlegrass populations. Its primary threat in the past was loss of habitat due to development in its preferred habitat of open, level, sandy land. Currently, major threats are from encroaching trees and shrubs that shade suitable habitat and the introduction of exotic species. Its habitats need to be kept open for this species to continue to thrive. Right-of-way maintenance may either threaten or assist this species to thrive and have acted as both in Massachusetts.
Conservation
Survey and monitoring
As with all rare species, it is helpful to know how the populations of this rare plant are doing, and regular surveys are important. Purple needlegrass is best surveyed when the seed is ripe on a dry, sunny day in September or October. This species forms clumps with numerous flowering ramets growing from one genet. When reporting to MassWildlife’s Natural Heritage and Endangered Species Program (NHESP), please note whether you are reporting genets (individual plants) or ramets (individual flowering stems).
Management
Purple needlegrass thrives in open areas. Such openings are maintained through mowing, prescribed fire and occasionally through grazing with goats. Exotic species may be a threat and assessment of those followed by management may be required. All management activities within purple needlegrass habitat, including removal of exotic species, needs to be discussed with NHESP, and possibly permitted first.
Research needs
The exact ecological needs for purple needlegrass are not known, and more research is needed. This species has declined severely across the state. Part of that decline is known (see above) but open habitats exist that seem appropriate where it has not been observed. The length of seed viability in appropriate habitats is also unknown, as is whether opening suitable habitat, through a reduction in canopy cover, will allow the species to grow there again. Other uncertainties include: Can this species be grown and then transplanted into appropriate areas? Would direct seed or planting seedlings into appropriate habitat improve the success of a restored population? Lastly, expansion and contraction of the awns due to humidity is thought to lead to the self-burial of seeds, but this has not been proven in the field. It was observed in greenhouse studies with a related species (Collins and Wein 1987).
References
Clarke, Gretel L. and William A. Patterson III. “The distribution of disturbance-dependent rare plants in a coastal Massachusetts sandplain: Implications for conservation and management.” Biological Conservation. 136 (2007) 4 – 1 6.
Haines, Arthur. Flora Novae Angliae. New England Wild Flower Society, Yale University Press, 2011.
Gleason, Henry A., and Arthur Cronquist. Manual of Vascular Plants of Northeastern United States and Adjacent Canada, Second Edition. Bronx: The New York Botanical Garden, 1991.
NatureServe. 2025. NatureServe Network Biodiversity Location Data accessed through NatureServe Explorer [web application]. NatureServe, Arlington, Virginia. Available https://explorer.natureserve.org/. Accessed: 2/17/2025.
POWO (2025). "Plants of the World Online. Facilitated by the Royal Botanic Gardens, Kew. Published on the Internet; https://powo.science.kew.org/ Retrieved 17 February 2025."
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| Date published: | March 20, 2025 |
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