Lechea stricta (Prairie Pinweed)

Plant Info
Also known as: Bushy Pinweed
Genus:Lechea
Family:Cistaceae (Rockrose)
Life cycle:perennial
Origin:native
Habitat:part shade, sun; dry sandy or rocky soil; prairies, dunes, rock outcrops, bluffs, creek banks, jack pine stands, open woods
Bloom season:July - September
Plant height:10 to 18 inches
Wetland Indicator Status:none
MN county distribution (click map to enlarge):Minnesota county distribution map
National distribution (click map to enlarge):National distribution map

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Detailed Information

Flower: Flower shape: 3-petals Flower shape: indistinct Cluster type: panicle

[photo of flowers] Numerous tiny, stalked flowers along branching stems, the whole cluster a third to half the height of the plant and the branches all ascending to erect. Flowers are not often seen open, usually closed and appearing bud-like. Open flowers have 3 short, reddish petals, a pompom-like cluster of stigmas, and 5 or more stamens.

[close-up of calyx] The calyx surrounding the flower is less than 1/8 inch (1.6 to 1.8 mm) long with 5 sepals in 2 series. The 3 inner sepals are broadly egg-shaped and dark red; the 2 outer sepals are green, linear, and usually shorter than the inner sepals. Flower stalks and sepals are all moderately to densely covered in straight, appressed white hairs.

Leaves and stems: Leaf attachment: alternate Leaf type: simple

[photo of leaves] Leaves are alternate to nearly opposite, mostly linear, up to about ¾ inch (13 to 20 mm) long, up to 1/8 inch (1.5 to 3 mm) wide, toothless, pointed at the tip, and stalkless. Most leaves below the flower cluster drop off early; leaves on the flowering branches are persistent but tend to be smaller.

[close-up of hairs on the lower leaf surface] The upper leaf surface is hairless or has a few straight appressed hairs, the lower surface is sparsely to densely covered in appressed hairs with the densest hairs along the midvein and edges. Stems are multiple from the base, often abruptly erect from near the base, unbranched except in the flower clusters, and covered in appressed hairs, more sparsely so at the base and denser into the flower clusters. In late summer, several short, leafy shoots radiate from the base.

Fruit: Fruit type: capsule/pod Fruit type: seed without plume

[photo of fruit] Fruit is a round capsule less than 2 mm wide and about as long as the inner sepals, containing 3 or 4 smooth, brown seeds.

Notes:

Prairie Pinweed is the most common of the 3 Lechea species known to be in Minnesota, though distinguishing this from Intermediate Pinweed (Lechea intermedia) can be quite the challenge.

Nearly every reference notes the hairiness can distinguish one from the other: L. stricta is more densely hairy, more gray-green, and the lower leaf surface densely hairy, while L. intermedia is less hairy, more green, and the lower leaf surface hairless or hairy only on the midvein and edges. However, Flora of North America notes: "Some individuals of Lechea stricta can be difficult to determine with certainty; the extremes of variation of L. stricta often grade into that of L. intermedia". Concerning hairiness, Michigan Flora also notes: "differences defy any quantitative statement". Indeed.

Having inspected dozens of populations around the state, we have yet to see any plant with dense hairs across the lower leaf surface. All have had hairs along the midvein and edges, but the surface between those zones rarely has more than a few sparse hairs, and overall plants may look green, grayish, or any shade in between. It appears both may have flowering stems that abruptly become erect from near the base. The more telling difference is likely mature fruit, where L. stricta has 3 or 4 brown seeds per capsule and L. intermedia 4 to 6 light to medium brown seeds that are irregularly covered in a thin, grayish, veiny coating.

Going just by the number of seeds, I can't say with any confidence we've encountered L. intermedia anywhere in the state. Revisiting sites described in herbarium records has not yielded the desired results and none of the reports on iNaturalist from Minnesota or Wisconsin that I've looked at show what I would consider distinctive characteristics for a positive ID, but we are still looking.

Prairie Pinweed is more easily distinguished from Narrowleaf Pinweed (Lechea tenuifolia), a rare species which has the 2 outer sepals much longer than the inner 3. Fruiting Frostweeds (Crocanthemum [syn. Helianthemum] spp.) may bear some resemblance to Lechea, but have stems and leaves covered in short, star-shaped hairs, not straight, appressed hairs.

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More photos

Photos by K. Chayka taken in Anoka, Ramsey, Wadena and Washington counties. Photos by Peter M. Dziuk taken in Anoka and Ramsey counties.

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