Micranthes pensylvanica var forbesii (Vasey) Bush

Forbes' Saxifrage

Micranthes pensylvanica var. forbesii plant

Family - Saxifragaceae

Stems - Leaves and aerial stems arising from a caudex. Roots fleshy and translucent.

Leaves - Leaves in a basal rosette, spatulate, pilose above and below, less so above, tapered at the base to a reddish-purple short petiole, crenate to crenulate, rounded to acute at the apex, to +25cm long, +8cm broad.

Micranthes pensylvanica var. forbesii leaves

Micranthes pensylvanica var. forbesii basalsBasal leaves.

Inflorescence - Panicle of clustered cymules terminating the flowering scape. Each branch of the panicle subtended by a linear-oblong bract. Bracts reduced upward, glandular pilose abaxially, glabrous adaxially, entire. Peduncles of cymules densely glandular hirsute, the glands reddish (use a lens to see). Each division of the cymules and each flower subtended by a small bract. Pedicels of the flowers +/-2mm long in flower. glandular-hirsute as the peduncles.

Micranthes pensylvanica var. forbesii inflorescenceInflorescence.

Micranthes pensylvanica var. forbesii stemPubescence of the scape.

Flowers - Petals 5, white to greenish, distinct, lanceolate, glabrous, acute, 5mm long, to 1.5mm broad. Stamens 10, arising at the base of the petals and sepals, distinct, spreading to erect. Filaments translucent-white, to 1.5mm long, glabrous. Anthers orange when fresh, .4-.5mm long. Styles 2, expanded greatly at the base, divided all the way to the base, recurving at the apices, to 2mm long, glabrous, green. Stigmas small, translucent. Ovary swollen, green, glabrous, partially inferior, 2-carpeled. Placentation axile. Hypanthium pale green, obconic, 2-2.5mm long, glabrous. Sepals 5, green, glabrous, spreading, to 3mm long, 1.5mm broad, subulate, with reddish apices.

Micranthes pensylvanica var. forbesii calyxCalyx.

Micranthes pensylvanica var. forbesii flowerFlowers.

Micranthes pensylvanica var. forbesii flowerSingle flower.

Fruits - Capsules 3.5-5.5 mm long, ovoid, 2-beaked, dehiscing longitudinally along the inner suture of each beak, the free tips divergent.

Micranthes pensylvanica var. forbesii fruitsFruits.

Flowering - April - June.

Habitat - Moist, north-facing sandstone bluffs. Typically on St. Peter sandstone but sometimes found on other types of sandstone.

Origin - Native to U.S.

Other info. - This species can be found in the east-central portion of Missouri and is fairly exclusive to the habitat mentioned above. The plants grow directly from the sides of cracks in the sandstone or in the thin layer of litter settled upon the rock. The basal leaves of the plant emerge very early in the spring and flowering occurs about a month later.
This is an easy species to identify becasue of its habitat, pilose stems, and big basal leaves.

Photographs taken at Danville Conservation Area, Montgomery County, MO., 4-8-04 (DETenaglia); also at Klondike County Park, St. Charles, MO, 5-6-2013, and Danville Conservation Area, Montgomery County, MO, 4-25-2017 and 5-6-2017 (SRTurner).


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