Synonyms

Lechea tenuifolia var. occidentalis

  Basis for Listing

Lechea tenuifolia (narrow-leaved pinweed) occurs in much of central and southeastern U.S., but has been documented at very few locations in southeast (The Blufflands Subsection) and east-central (St. Paul-Baldwin Plains and Moraines and Oak Savanna subsections) Minnesota. One is a historical population in Rice County (Big Woods Subsection) that is now believed to be extinct. In all cases, the habitat of this species in Minnesota is high-quality sand prairie or sand savanna. Maintaining healthy sand prairie and sand savanna habitat requires active management such as prescribed fire to maintain conditions suitable for L. tenuifolia. Potentially conflicting land uses and increasing pressure for residential development may make such land management difficult. With these threats and so few populations, the species' survival in Minnesota is tenuous. For these reasons, L. tenuifolia was listed as a state endangered species in 1996.

  Description

Typical plants are 10-25 cm (4-10 in.) tall, though the stems often do not stand erect. Even though the plant is small, the numerous closely-spaced stems may give the plant a bushy appearance. Foliage of L. tenuifolia is grayish green, with soft short downy hairs on the underside of the leaves. The leaves are opposite or whorled on the stem, very slender and short. The flowers are numerous, minute, red, and borne singly toward the ends of tertiary branches. They are rarely noticed, because they are so small (about 2 mm [0.8 in.] long and may resemble pinheads) and rarely open. Flowers have 3 petals that are shorter than the 5 sepals. The 2 outer sepals are as long as or longer than the 3 inner sepals. The fruit is a dry capsule less than 2 mm (0.8 in.) long, each with 2-3 tiny seeds (Barringer 2004; Spalding 2013).

The other two Minnesota species of Lechea, L. intermedia (intermediate pinweed) and L. stricta (prairie pinweed), differ in that the 2 outer sepals are noticeably shorter than the 3 inner sepals (Gleason and Cronquist 1991).

  Habitat

In Minnesota, L. tenuifolia inhabits dry sandy prairies or openings in sand savannas. These are fire-maintained habitats, indicating that L. tenuifolia is fire-dependent or at least fire-adapted. The droughty nature of the soil results in small patches of open sand where there is little competing vegetation. Associated species include Cyperus lupulinus (slender nut sedge), Koeleria macrantha (Junegrass), and Solidago nemoralis (gray goldenrod).

  Biology / Life History

Lechea tenuifolia is apparently perennial, though it is sometimes described as being biennial at northern latitudes (Barringer 2004). It is a rare event for the tiny flowers of L. tenuifolia to open, but it is alleged that they will open in the early morning light of bright days. It reproduces only by seed. Each fruit has 2-5 seeds, which possess no obvious mechanism to facilitate long-distance dispersal. Short-range seed dispersal is likely passive or facilitated by small animals, possibly including seed-caching mammals. The seeds of a closely related species have been reported to remain viable in the soil for at least 15 years and germinate after being exposed to high temperatures such as might occur during a typical grass fire (Crisfield et al. 2019).

  Conservation / Management

The type of dry sandy prairies that contain L. tenuifolia are often threatened by agricultural conversion, shrub and tree encroachment, noxious weed invasion, and residential development. Although L. tenuifolia habitats may not be prime for housing development, the increasing demand for real estate has resulted in the development of relatively marginal sites in recent years, and the trend seems to be continuing. One of the L. tenuifolia sites found in recent years is on an abandoned railroad right-of-way that has been coming under significant development and agricultural pressure in recent decades. It is essential that prairie remnants, including those in railroad rights-of-ways be protected. Management could include prescribed spring burns, manual or mechanical cutting of encroaching woody vegetation, and removal of invasive non-native species.

  Best Time to Search

The time to search for Lechea tenuifolia is from June through September, but primarily while it is in bloom, July through August.

  Conservation Efforts in Minnesota

The Washington County population of L. tenuifolia occurs on both a Scientific and Natural Area and a Wildlife Management Area, which offers some conservation protection for the species and its habitat.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(Note: all content ©MNDNR)

  References and Additional Information

Barringer, K. 2004. New Jersey pinweeds (Lechea, Cistaceae). Journal of the Torrey Botanical Society 131(3):261-276.

Crisfield, V. E., D. L. Haughland, and L. A. Pyle. 2019. Reproductive ecology of impoverished pinweed (Lechea intermedia var. depauperata), a fire-associated narrow endemic from the boreal forest. Botany 97(10):559-570.

Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.

Hodgdon, A.R. 1938. A taxonomic study of Lechea. Rhodora 40: 29-69.

Lemke, D. E. 2015. Lechea. Pages 389-397 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexcio. Volume 6. Oxford University Press, New York, New York.

Spaulding, D. D. 2013. Key to the pinweeds (Lechea, Cistaceae) of Alabama and adjacent states. Phytoneuron 99:1-15.

The Great Plains Flora Association. 1986. Flora of the Great Plains. University Press of Kansas, Lawrence. 1,402 pp.