Onosmodium molle Michx.

Western False Gromwell

Onosmodium molle plant

Family - Boraginaceae

Habit - Perennial forb with stout, woody rootstock.

Stem - Arched to ascending, to 1.2 m, sometimes multiple, sometimes branched, glabrous to densely hairy.

Onosmodium_molle_stem.jpgLower stem.

Onosmodium_molle_stem2.jpgUpper stem.

Leaves - Alternate, simple, sessile or nearly so. Lowest leaves withered and absent at flowering. Blades 2-14 cm long, 10-40 mm wide, lanceolate to ovate, angled or tapered at the base, angled or tapered to a sharply pointed tip, the upper surface densely pubescent with appressed to spreading, stiff, pustular-based hairs, the undersurface moderately to densely pubescent with softer, sometimes nonpustular-based hairs, with 2-4 prominent pairs of lateral veins, these usually strongly impressed on the upper surface and strongly ridged on the undersurface.

Stem and leaves.

Onosmodium_molle_leaf1.jpgLeaf adaxial.

Onosmodium_molle_leaf2.jpgLeaf abaxial.

Inflorescence - Often paired, terminal, appearing as dense clusters at the start of flowering, becoming elongated into scorpioid, spikelike racemes, the flowers with stalks 0.3-1.0 mm long at flowering, these elongating to 1.5-3.0 mm at fruiting, ascending, each flower subtended by a leaflike bract 10-35 mm long.


Onosmodium_molle_inflorescence2.jpgScorpioid inflorescence.

Flowers - Calyces actinomorphic, 5-lobed nearly to base, the lobes 3.5-9.0 mm long at flowering, elongating slightly at fruiting, linear to narrowly narrowly oblanceolate, densely hairy on both surfaces, persistent and ascending at fruiting. Corollas 7-16 mm long at full flowering, tubular with a small bulge in the throat, actinomorphic, white to cream-colored or greenish yellow, hairy on the outer surface, the tube 5-12 mm long, the lobes 2-4 mm long. Stamens inserted near the tip of the corolla tube, the filaments very short, not or only slightly exserted from the corolla. Ovary deeply 4-lobed, the style elongate, strongly exserted from the corolla, persistent at fruiting, stigma capitate, shallowly 2-lobed.



Fruits - Schizocarps dividing into mostly 1 or 2 nutlets, these 2.5-5.0 mm long, ovoid, sometimes with a shallow ventral groove or an indistinct, blunt ventral ridge, white to ivory-colored or brownish-tinged, attached to the flat gynobase at the base, the attachment scar relatively large, the surface smooth or rarely minutely pitted, sometimes shiny.

Onosmodium_molle_fruits.jpgImmature fruits.

Flowering - May - August.

Habitat - Glades, savannas, forests, bluff tops, prairies, fields, roadsides, often on calcareous substrate.

Origin - Native to the U.S.

Lookalikes - Broadly, Lithospermum latifolium

Other info. - This interesting and striking species is fairly common in Missouri, found predominantly in the southern 2/3 of the state. The subspecies pictured above, ssp. subsetosum, is quite limited in its U.S. distribution, being almost entirely confined to Missouri and states adjacent to the south. In Missouri this is the most common of the three subspecies present in the state.

Onosmodium molle is a plant of somewhat subtle beauty. The flowers are small and not particularly showy, though they are unusual and interesting up close. Perhaps the showier and more distinctive parts of the plant are the leaves, which are prominently veined. The conspicuous texture of the leaf reflects both the strongly impressed venation and the whitish appressed hairs. This was one of Dan Tenaglia's favorite Missouri species. Though its attractiveness is understated, this plant is well deserving of cultivation.

As noted above, there are three subspecies of the plant recognized in Missouri. The ssp. subsetosum pictured above has stems which are glabrous near the base of the plant and hairy near their tips. The other forms, ssp. hispidissimum and ssp. occidentale, have uniformly hairy stems, and differ in other aspects of fruits and leaf hairs. Onosmodium taxonomy is somewhat unsettled, and some authors have elevated these forms to the species level and placed them in the genus Lithospermum. By this reckoning, the taxon applied to the plant shown on this page is Lithospermum subsetosum.

Photographs taken at Cuivre River State Park, Lincoln County, MO, 6-13-2009, St. Joe State Park, St. Francois County, MO, 5-25-2010 and 6-10-2013, Shaw Nature Reserve, Franklin County, MO, 6-18-2011, and Little Lost Creek Conservation Area, Warren County, MO, 6-3-2018 and 6-10-2019 (SRTurner).