This perennial wildflower is 2-3½' tall and either unbranched or sparingly branched. The central stem and any lateral stems are medium green, terete, and sparsely short-pubescent. The alternate leaves are trifoliate; their petioles are 2-6' long, somewhat angular, medium green, and sparsely short-pubescent. At the base of each petiole, there is a pair of stipules about 8 mm. (0.3') long; they are linear-lanceolate in shape and early-deciduous. The leaflets of the trifoliate leaves are 2-4' long and 1-2' across; they are lanceolate-ovate to ovate in shape, while their margins are smooth (entire) and slightly ciliate. The bases of these leaflets are rounded, while their tips are rather slender and pointed. The upper leaflet surface is medium green and sparsely short-pubescent to glabrous, while the lower leaflet surface is pale to medium green and sparsely short-pubescent. Leaflet venation is pinnate. The terminal leaflets have petiolules (basal stalklets) about ½-1' long, while the petiolules of the lateral leaflets are less than 1/8' in length. Both axillary and terminal racemes of flowers are produced on peduncles about 2-8' in length. These racemes are 2-6' long and spike-like in appearance; the density of flowers along each raceme is intermediate. The central stalk of each raceme is pale green and sparsely covered with short fine pubescence. Each flower is about ¼' long and relatively narrow in shape, consisting of 5 blue, purple, or nearly white petals, a short-tubular calyx with 5 teeth, and the reproductive organs. The petals form an upright banner, a pair of forward-projecting wings, and a small keel that is largely hidden by the wings. At the base of the banner, there is a small patch of yellow with fine purple veins. The calyx is pale green to pale purplish yellow and sparsely short-pubescent. The pedicels of the flowers are very short (less than 1/8' in length). The blooming period occurs from late spring to mid-summer, lasting about 1 month. Afterwards, the flowers are replaced by short seedpods about 8-12 mm. long. These seedpods are obovoid, somewhat compressed (flattened), and asymmetric (more curved on one side than the other); they are single-seeded. Individual seeds are 4-6 mm. long, reniform (kidney-shaped), and somewhat compressed, becoming dark brown at maturity. The root system is rhizomatous, often forming clonal colonies of plants.

The native French Grass is uncommon to occasional in central Illinois, becoming rare or absent in the southern and northern sections of the state (see Distribution Map). It is found primarily in the lower Midwest (Illinois, Indiana, Ohio, and eastern Missouri). Habitats include black soil prairies, pioneer cemetery prairies, lower slopes of hill prairies, riverbanks, upland open woodlands, poorly maintained embankments along country roads, and fallow fields. French Grass is found in both high quality habitats (mostly prairie remnants) and more disturbed habitats that have a history of neglect.

Psoralea onobrychis Nutt.:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

Orbexilum onobrychis (Nutt.) Rydb.:
United States (North America)

Note: This information is based on publications available through Tropicos and may not represent the entire distribution. Tropicos does not categorize distributions as native or non-native.

United States

Origin: Unknown/Undetermined

Regularity: Regularly occurring

Currently: Unknown/Undetermined

Confidence: Confident

Perennial, Herbs, Stems woody below, or from woody crown or caudex, Plants with rhizomes or suckers, Nodules present, Stems erect or ascending, Stems less than 1 m tall, Stems solid, Stems or young twigs glabrous or sparsely glabrate, Stems or young twigs sparsely to densely hairy, Leaves alternate, Leaves petiolate, Stipules conspicuous, Stipules setiform, subulate or acicular, Stipules deciduous, Stipules free, Leaves compound, Leaves pinnately 3-foliolate, Leaves odd pinnate, Leaf or leaflet margins entire, Leaflets opposite, Leaflets 3, Leaves glandular punctate or gland-dotted, Leaves glabrous or nearly so, Inflorescences racemes, Inflorescence axillary, Bracts very small, absent or caducous, Flowers zygomorphic, Calyx 5-lobed, Calyx hairy, Petals separate, Corolla papilionaceous, P etals clawed, Petals blue, lavander to purple, or violet, Banner petal ovoid or obovate, Banner petal auriculate, Wing petals narrow, oblanceolate to oblong, Wing tips obtuse or rounded, Keel tips obtuse or rounded, not beaked, Stamens 9-10, Stamens diadelphous, 9 united, 1 free, Filaments glabrous, Style terete, Style sharply bent, Fruit a legume, Fruit unilocular, Fruit indehiscent, Fruit oblong or ellipsoidal, Fruit rugose wrinkled or reticulate, Fruit exserted from calyx, Fruit beaked, Fruit glabrous or glabrate, Fruit 1-seeded, Seeds reniform, Seed surface smooth, Seeds olive, brown, or black.

The native French Grass is uncommon to occasional in central Illinois, becoming rare or absent in the southern and northern sections of the state (see Distribution Map). It is found primarily in the lower Midwest (Illinois, Indiana, Ohio, and eastern Missouri). Habitats include black soil prairies, pioneer cemetery prairies, lower slopes of hill prairies, riverbanks, upland open woodlands, poorly maintained embankments along country roads, and fallow fields. French Grass is found in both high quality habitats (mostly prairie remnants) and more disturbed habitats that have a history of neglect.

Aside from flower-visiting insects, very little is known about floral-faunal relationships for this species. Robertson (1929) observed honeybees, bumblebees, cuckoo bees (Coelioxys spp.), leaf-cutter bees (Megachile spp.), mason bees (Osmia spp.) Halictid bees, plasterer bees (Colletes spp.), Sphecid wasps, Vespid wasps, bee flies (Bombyliidae), thick-headed flies (Conopidae), butterflies, skippers, and moths visiting the flowers for nectar. Some of the bees also collected pollen from the flowers. Robertson also observed an uncommon carder bee, Anthidium psoralaeae, visiting the flowers of French Grass. This latter bee is an oligolege (specialist pollinator) of some prairie species (Orbexilum spp., Psoralidium spp., etc.) in the Bean family. There is also a newly discovered, but still unnamed, moth caterpillar (Schinia sp.) that feeds on French Grass in the lower Midwest. This caterpillar is pale yellowish green with pairs of large black dots along its sides.

Psoralea onobrychis (Sanfoin)
(Also referred to as French Grass and Orbexilum onobrychis; bees collect pollen or suck nectar; other insects suck nectar, except where it is otherwise indicated [fsp = feeds on stray pollen]; butterflies, skippers, & moths are non-pollinating; observations are from Robertson)


Bees (long-tongued)
Apidae (Apinae): Apis mellifera sn fq; Apidae (Bombini): Bombus auricomus sn, Bombus fraternus sn, Bombus griseocallis sn cp fq, Bombus impatiens sn, Bombus pensylvanica sn; Anthophoridae (Ceratinini): Ceratina dupla dupla sn; Anthophoridae (Epeolini): Epeolus interruptus sn; Anthophoridae (Eucerini): Florilegus condigna sn, Melissodes bimaculata bimaculata sn, Synhalonia speciosa sn; Megachilidae (Anthidinini): Anthidium psoraleae sn fq olg; Megachilidae (Coelioxini): Coelioxys germana sn, Coelioxys modesta sn fq, Coelioxys octodentata sn fq, Coelioxys sayi sn fq; Megachilidae (Megachilini): Megachile addenda sn cp fq, Megachile brevis brevis sn cp fq, Megachile campanulae campanulae sn fq, Megachile latimanus sn, Megachile mendica sn cp fq, Megachile petulans sn fq, Megachile rugifrons sn cp fq, Megachile texana sn cp fq; Megachilidae (Osmiini): Hoplitis pilosifrons sn cp, Osmia atriventris sn, Osmia conjuncta sn

Bees (short-tongued)
Halictidae (Halictinae):Agapostemon sericea sn cp, Halictus confusus sn icp, Halictus rubicunda sn, Lasioglossum cinctipes sn, Lasioglossum coriaceus sn; Colletidae (Colletinae): Colletes brevicornis sn fq, Colletes eulophi sn cp fq icp; Andrenidae (Panurginae): Calliopsis andreniformis sn cp fq icp

Wasps
Sphecidae (Sphecinae): Eremnophila aureonotata, Prionyx atrata, Prionyx thomae; Vespidae: Polistes dorsalis; Vespidae (Eumeninae): Euodynerus annulatus, Pterocheilus quinquefasciatus

Flies
Syrphidae: Tropidia mamillata sn; Bombyliidae: Bombylius atriceps sn, Exoprosopa fasciata sn, Hemipenthes sinuosa fsp, Rhynchanthrax parvicornis sn; Conopidae: Physocephala tibialis sn, Stylogaster biannulata sn

Butterflies
Pieridae: Pontia protodice; Papilionidae: Battus philenor

Skippers
Hesperiidae: Epargyreus clarus, Erynnis juvenalis

Moths
Sphingidae: Hemaris thysbe; Noctuidae: Schinia sp.

The following is a representative barcode sequence, the centroid of all available sequences for this species.


No available public DNA sequences.

Download FASTA File

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 2
Specimens with Barcodes: 2
Species With Barcodes: 1

United States

Rounded National Status Rank: NNR - Unranked

Rounded Global Status Rank: G5 - Secure

The preference is full or partial sun, mesic to dry-mesic conditions, and loamy soil. This wildflower can be propagated by seed or division of its rhizomes.