Senecio plattensis Nutt. - Prairie Ragwort

Senecio plattensis plant

Family - Asteraceae

Stems - To 50cm tall, simple to branching near apex, fistulose, erect, with dense arachnoid pubescence below and also scattered along the stem and in the axils of the branches and leaves, with shallow ridges, from slightly thickened roots.

Senecio plattensis stemLower stem.

Leaves - Alternate. Basal leaves long petiolate. Petioles to +10cm long, densely arachnoid pubescent at base and less so above. Blade undivided, elliptic-lanceolate to elliptic-ovate, to 6.5cm long, 2.5cm broad, serrate, villosuous below to glabrous, thickened (subsucculent). Cauline leaves deeply divided (pinnatifid to bipinnatifid), petiolate below, becoming sessile above, densely arachnoid pubescent at base, with scattered arachnoid pubescence on rest of leaf or appearing glabrous on lobes, thickened (subsucculent). Lobes typically shallowly lobed again, entire.

Senecio plattensis leavesMiddle and upper leaves of stem.

Inflorescence - Numerous flower heads in a corymbiform cyme terminating stems. Branches of inflorescence with floccose-arachnoid pubescence in axils. Peduncles with minute linear bracts often subtending flower heads.

Involucre - Cylindrical, 6-7mm tall(long), 6-7mm in diameter, truncate at base. Phyllaries in a single series, connate for most of length, arachnoid pubescent at least at base, with scarious acuminate tips.

Senecio plattensis involucreInvolucre.

Ray flowers - Typically 13 per flower head, fertile. Ligules to 1cm long, 3mm broad, truncate or with a shallow notch at apex, orangish-yellow. Achenes densely clavate pubescent. Pappus of barbed capillary bristles to 5mm long.

Disk flowers - Disk to 8mm in diameter. Flowers fertile. Corollas orange-yellow, 5-lobed. Lobes acute. Achenes clavate pubescent. Pappus of numerous barbed capillary bristles. Receptacle flat.

Senecio plattensis flower

Flowering - May - June.

Habitat - Dry upland prairies, bluffs, rocky open woods, glades, loess hills.

Origin - Native to U.S.

Other info. - This species can be found scattered throughout Missouri. It may be difficult to distinguish from some other species of Senecio but the dense arachnoid pubescence at the base of the stems and leaves and in the inflorescence is a good characteristic to look for. Also, the leaves will typically have some pubescence at least abaxially. The basal leaves are also undivided in this species.

Photographs taken off Hwy U in Benton County, MO., 5-15-04.


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