Rare Species Guide

  Synonyms

Triplasis purpurea

  Basis for Listing

As of 2010 there have been fewer than 10 discoveries of Triplasis purpurea var. purpurea in Minnesota, and it is likely that only four of those represent extant, viable populations. All four are from dune fields with native prairie or savanna vegetation. Dune habitats are quite rare in Minnesota as many were converted to conifer plantations after the dust bowl drought of the 1930s in an attempt to stabilize soil. However, these plantations resulted in the destruction of savanna and prairie habitats that supported T. purpurea var. purpurea and many other rare or declining species. A number of dune fields have also been converted to golf courses and housing developments, developed as landfills, or suffered from ill-advised attempts at agriculture. Even among the few remaining intact dune fields, few support populations of T. purpurea var. purpurea. For these reasons, T. purpurea var. purpurea was listed as a special concern species in Minnesota in 1984.

  Description

There are two species of Triplasis in North America, but only T. purpurea var. purpurea occurs in Minnesota. It is a tufted annual with ascending stems 14-100 cm (5.5-39.4 in.) long, with hairy nodes and smooth internodes. The leaves have a 1 mm (0.04 in.) long hairy ligule and a 1-5 mm (0.04-0.20 in.) wide flat or involute blade. The primary inflorescence is a terminal chasmogamous panicle (cleistogamous panicles are also produced but are enclosed within the leaf sheaths at the nodes) 3-7 cm (1.2-2.8 in.) long and 1-6 cm (0.4-2.4 in.) wide. It is sometimes partially enclosed in the upper leaf sheath. The spikelets are purplish, 6.5-9 mm (0.26-0.35 in.) long, and have 2-5 florets; they are laterally compressed and have a prolonged rachis. The flowers have 2 glumes, each about 2 mm (0.08 in.) long; they are glabrous or scabrous and shorter than the first lemma. The lemmas are 3-4 mm (0.12-0.16 in.) long, 3-veined, the veins hairy, and the midvein extended into a straight awn less than 2 mm (0.08 in.) long. The paleas are about 2.5 mm (0.10 in.) long and have hairy keels (Hatch 2003).

  Habitat

It is not known with absolute certainty, but it appears that the habitat of T. purpurea var. purpurea in Minnesota is restricted to sand dunes. There are a few older herbarium specimens with ambiguous labels, which were collected in non-specified sandy habitats that may or may not have been actual dunes. Still, it seems likely that viable populations are currently restricted to sand dunes. These are naturally occurring formations that support a highly specialized community of native plant species. The plant communities that develop on dunes are often classified as dry savannas (northern and southern) or dry prairies (northern and southern). However, T. purpurea var. purpurea is found only where such communities contain active sand dunes. The low fertility and poor water-holding capacity of the sand results in a very sparse plant cover with only a few scattered plants and large expanses of bare sand.

  Biology / Life History

Triplasis purpurea var. purpurea is an early successional dune species that thrives only where there is open sand and frequent disturbance (Cheplick and Demetri 2000). The primary source of disturbance in Minnesota habitats is wind, which results in constantly shifting sand. Experiments have shown that growth and reproduction are actually stimulated when seedlings are partially buried with sand compared to seedlings that have not been buried. It has also been shown that seedlings of T. purpurea var. purpurea can emerge if the seeds are buried in sand as deep as 6 cm (2.4 in.) (Cheplick and Grandstaff 1997). Seed production is reported to be high (Cheplick 2006), although the seed bank in the soil is apparently only transient. In one study, the depletion of the seed bank was over 90% during the course of a season (Cheplick 2006).

These life history traits are perhaps typical of species that inhabit sand dunes. There is, however, at least one unusual aspect to the reproductive biology of T. purpurea var. purpurea. It is one of a handful of grass species that is known to produce cleistogamous flowers in addition to the more conventional chasmogamous flowers. Chasmogamous flowers have their full complement of structural features and are designed for cross-pollination. They appear in an open panicle at the top of the stem. Cleistogamous flowers, on the other hand, are morphologically reduced and are designed for self-pollination. They are concealed in the leaf sheaths at the nodes of the stem. The stem is designed to break apart at the nodes allowing each segment, and its enclosed cleistogamously-produced seeds, to be dispersed independently (Chase 1908). Although this is seen as a way for the plant to "hedge its bets" in a reproductive sense, the ecological implications of this type of reproduction are not known (Cheplick 1996).

The best time to search for this species is late summer through fall, when the terminal panicle is fully developed.

  Conservation / Management

Although disturbance is needed to maintain the sand dune habitat of this species, it should not be assumed that all sources of disturbance have the same effect. Triplasis purpurea var. purpurea is adapted to wind disturbance and will not respond positively to disturbances caused by digging, trenching, road building, or the actions of off-highway vehicles. If conifers have been planted anywhere on or in the immediate vicinity of dune habitats, they should be immediately and carefully removed.

  Conservation Efforts in Minnesota

Triplasis purpurea var. purpurea is known to occur at three Scientific and Natural Areas including Grey Cloud Dunes SNA, Agassiz Dunes SNA, and Kellogg-Weaver Dunes SNA. The management goals of these sites, if adhered to, should be adequate to preserve the habitat of T. purpurea var. purpurea.

  References and Additional Information

Chase, A. 1908. Axillary cleistogenes in some American grasses. Botanical Gazette 45:135-136.

Cheplick, G. P. 1996. Cleistogamy and seed heteromorphism in Triplasis purpurea (Poaceae). Bulletin of the Torrey Botanical Club 123(1):25-33.

Cheplick, G. P. 2006. Seed rain, transient seed banks, and seedling recruitment of annuals on a coastal beach. Journal of the Torrey Botanical Society 133(3):379-392.

Cheplick, G. P., and H. Demetri. 2000. Population biology of the annual grass Triplasis purpurea in relation to distance from shore on Staten Island, New York. Journal of Coastal Conservation 5:145-154.

Cheplick, G. P., and K. Grandstaff. 1997. Effects of sand burial on purple sandgrass (Triplasis purpurea): the significance of seed heteromorphism. Plant Ecology 133:79-89.

Hatch, S. L. 2003. Triplasis. Pages 41-42 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 25, part 2. Oxford University Press, New York, New York.