Cistaceae (Rock Rose family)
Description: This perennial plant is ½–1½' tall and abundantly branched, particularly along the upper two-thirds of its length. The pale green stems are sparsely to moderately covered with white hairs that are upwardly appressed or ascending. Small leaves about 8-15 mm. (1/3–2/3") long and about one-third as much across occur along the stems: they are alternate, opposite, or whorled. The leaf blades are green (turning yellow during the fall), smooth and ciliate along their margins, and elliptic-oblong with blunt tips; the base of each leaf blade is sessile, or it is has a short petiole. The upper surfaces of the blades are hairless to sparsely hairy, while the lower surfaces of the blades are usually hairy, particularly along the midveins. Similar to the hairs on the stems, the hairs on the leaves are appressed or curve outward toward their tips. The middle to upper stems produce overlapping panicles of flowers. Individual panicles are longer than they are wide, and they produce leafy bracts that are similar to the leaves, except the former are smaller in size. The small flowers are borne individually on the secondary and tertiary branches of the panicles. Each flower is about 2 mm. long and a little less across, consisting of 5 persistent purplish red petals, 5 ascending green sepals (sometimes becoming red later), 3 or more stamens, and a 3-celled ovary with short stigmata at its apex (there are no filaments). Each flower has a short slender pedicel about 1 mm. long. The blooming period occurs during the late summer for about a month; only a few flowers are in bloom at the same time. The flowers are probably cross-pollinated by wind, at least in part. Each flower is replaced by an ovoid seed capsule about 2 mm. long that typically contains 2-3 seeds; because of the persistent petals and sepals, it is purplish red or greenish red in appearance. The 2 outer sepals are the same length or longer than the seed capsule (2 mm. in length or more) and they are linear in shape. The 3 inner sepals are shorter than the seed capsule (less than 2 mm. in length) and they are ovate in shape. After the seed capsules open, the small seeds are dispersed primarily by gravity and usually fall only a short distance from the mother plant. During the late fall, the flowering plant withers away and it is replaced by a low rosette of little-branched stems with whorled or opposite leaves; this rosette spans about 3-4" across and usually survives the winter until it is replaced by a flowering plant during the next spring. The basal leaves are similar to the cauline leaves of the flowering plant, except they are more wide in shape (oval-ovate). The root system consists of a slender taproot with fibrous secondary roots; sometimes the taproot is barely distinguishable from these secondary roots.
Cultivation: The preference is full or partial sun, moist to dry conditions, and either sandy or very rocky soil. The seeds are slow to germinate, often remaining dormant for several years.
Range & Habitat: The native Small Pinweed is an uncommon plant that is found in NE Illinois and scattered locations elsewhere in the state (see Distribution Map). Habitats include sand prairies, openings and edges of sandy oak woodlands, sandy oak savannas, rocky bluffs and cliffs, partially wooded sand dunes near Lake Michigan, and edges of sandy marshes. In many areas, populations of Small Pinweed have declined as a result of habitat destruction from various development projects. Like other Lechea spp. (Pinweeds), it is adapted to occasional disturbance (wildfires, shifting dunes), but dislikes extreme or more frequent modifications of its environment.
Faunal Associations: In general, very little is known about the floral-fauna relationships of Lechea spp. (Pinweeds); they have not been studied adequately, thus some of the following information is speculative. The flowers offer no nectar to insect visitors; only pollen is available as a food reward. It is possible that various flies, small bees, and other small insects are minor pollinators of the flowers, which are self-fertile and probably cross-pollinated by the wind. It has been found that White-Tailed Deer preferentially browse on Lechea maritima (Beach Pinweed) in Virginia (see Keiper, 1990), and thus they may browse on other Pinweeds in other areas as well.
Photographic Location: Edge of a sandy oak woodland that is located near a wet sand prairie at the Iroquois County Conservation Area in Iroquois County, Illinois.
Comments: In most of Illinois, Lechea spp. (Pinweeds) are restricted to sandy habitats, although in southern Illinois some species (including Small Pinweed) can be found along cliffs and upland woodlands that are rocky. The various species are very similar to each other in appearance and can be difficult to differentiate. The presence of mature fruits on a prospective plant greatly facilitates its identification and, to a lesser extent, the shape of the leaves and type of hairs on the stems facilitates species identification as well. Small Pinweed can be distinguished from other similar Pinweed species as follows: 1) it has wider leaves than some other species, which are more linear in shape, 2) the hairs on its stems are upwardly appressed or ascending, rather than widely spreading or absent, 3) the seed capsules are ovoid in shape, rather than globoid or subgloboid, and 4) the outer sepals of Small Pinweed are longer than the inner sepals and they are as long or longer than the seed capsules. The only other Pinweed in Illinois with the last characteristic is Lechea tenuifolia (Slender Pinweed), which differs by having linear leaves and it tends to be smaller in size. Another common name of Lechea minor is Thyme-Leaved Pinweed.