Isopyrum biternatum (Raf.) Torr. & A. Gray

False Rue Anemone

Isopyrum_biternatum_plant.jpg
STATS

Native
CC = 5
CW = 3
MOC = 60

© SRTurner

Family - Ranunculaceae

Habit - Perennial forb with slender, woody rhizomes.

Stems - Ascending to erect, to 35 cm, glabrous.

Isopyrum_biternatum_stem.jpg Stem and leaves.

This differs markedly from the true rue anemone, Thalictrum thalictroides, which has only a single node of bracts below the flower.

© SRTurner

Leaves - Alternate and basal, petiolate, ternately divided, glabrous. Basal leaves 2 or 3, on petioles to 12 cm long, glabrous. Stem leaves 1-4, progressively shorter-petiolate, the uppermost sometimes sessile or nearly so. Blades mostly twice ternately compound, those of the uppermost leaves sometimes only once ternate, the leaflets mostly 10-25 mm long, ovate to broadly lanceolate, deeply 2-or 3-lobed or-parted, the lobes rounded at the tip, sometimes again shallowly notched.

Isopyrum_biternatum_cauline_leaf.jpg Cauline leaf.

© DETenaglia

Isopyrum_biternatum_leaf2.jpg Leaf abaxial.

© SRTurner

Isopyrum_biternatum_leaf2a.jpg Leaf abaxial.

© SRTurner

Isopyrum_biternatum_stipules.jpg Petiolar appendages.

© SRTurner

Inflorescence - Solitary flowers or loose clusters, sometimes appearing as short, leafy racemes of 2-4 flowers. Flowers becoming more dense near the apex of the stems. Pedicels glabrous, to 1 cm long.

Flowers - Actinomorphic, perfect. Sepals 5 or 6, 6-12 mm long, distinct, petaloid, white, rarely pinkish-tinged, plane, entire, rounded at the apex, slightly tapered at the base, oblong-elliptic, glabrous, not persistent at fruiting. Petals absent. Stamens numerous, arising from below the carpels, mostly erect. Filaments white, glabrous, to 4 mm long, very thin, clavate. Anthers yellow, globose. Pollen white. Pistils 2-5 in a whorl, each with 2-6 ovules, glabrous. Style 2 mm long. Stigma minute.

Isopyrum_biternatum_flower2.jpg Sepals.

© SRTurner

Isopyrum_biternatum_flower.jpg Flower.

© SRTurner

Isopyrum_biternatum_sepals.jpg Sepals. Petals absent.

© SRTurner

Fruits - Follicles, obovate in outline, flattened, the body 4-5 mm long, tapered abruptly to a slender beak 1.5-2.0 mm long, the outer wall thick, prominently veined. Receptacle not much enlarged at fruiting.

Isopyrum_biternatum_fruits.jpg Fruits.

© SRTurner

Flowering - March - May, rarely also October.

Habitat - Bottomland and mesic forests, bluff bases, streambanks, ravines.

Origin - Native to the U.S.

Lookalikes - Thalictrum thalictroides.

Other info. - You know spring has arrived when you start to see this little plant bloom. It adds a splash of white to the woodland ground otherwise drab with leaves of fall and winter. The plant forms colonies with its horizontal creeping stems, and under favorable conditions these can cover large areas with a sea of the small white flowers. The plant is common in bottomland habitats across most of Missouri and the U.S. Midwest, and ranges into Canada as well.

The plant is easily recognized with a little practice, though it can be confused with the "true" rue anemone (Thalictrum thalictroides). There are several key differences between the two. Relative to the true anemone, Isopyrum biternatum has (usually) two leaves alternate per stem, rather than an opposite pair or whorl of bracts; flowers which are almost always white rather than pinkish or lavender tinged; usually 5 sepals per flower rather than 6-8 or more; a much more colonial growth habit; and a wetter habitat preference.

Another name for the plant is Enemion biternatum Raf. The species name refers to the leaves, which are (usually) "twice three-times divided" or biternate. The genus Isopyrum, assigned by Linnaeus, means roughly "like wheat," referring to the fruits.

Photographs taken at Whetstone Conservation Area, Callaway County, MO., 3-19-04, and at Eagle Bluffs Conservation Area, Boone County, MO., 3-27-04 (DETenaglia); also at Tyson County Park, St. Louis County, MO, 4-10-2011, Engelmann Woods Natural Area, Franklin County, MO, 4-12-2016, and Washington State Park, Washington County, MO, 4-24-2017 (SRTurner).