Arctium minus Bernh. - Burr Dock

Arctium minus plant

Family - Asteraceae

Stems - To 2m tall, herbaceous, branching, greenish to reddish-purple, sparse arachnoid pubescent to glabrous, from stout taproot.

Leaves - Alternate, petiolate. Petiole sparse arachnoid pubescent, with adaxial groove, to +40cm long, typically hollow. Basal leaves very large, to +60 cm long. Cauline leaves reduced upward,  truncate or cordate at base, ovate, with arachnoid pubescence below, puberulent above. Margins sinuous to undulate or commonly crisped.

Arctium minus leafBasal leaf and size 10 hiking boot.

Inflorescence - Loose pedunculate cymes of 1-4 flowers in upper leaf axils and terminating stems. Peduncles tomentose.

Involucre - (In flower) - To 1.3cm long(tall), +1cm in diameter, urceolate. Phyllaries linear-attenuate, uncinate and reddish at apex, to 1.5cm long, mostly glabrous but strigillose on margins near base. Involucre becoming slightly enlarged and globose in fruit.

Arctium minus plantInvolucre.

Ray flowers - Absent.

Disc flowers - Corolla tube to 1cm long, constricted and white below, rose-pink above, glabrous, 5-lobed. Lobes acute, 1.3mm long, glabrous. Stamens 5, adnate at apex of constricted portion of corolla tube. Filaments white, glabrous, 3.5mm long. Anthers purple, connate around atyle, exserted, 3mm long. Style bifurcate, white, pubescent at base of stigmas. Achenes to 2.5mm long in flower(6mm in fruit), whitish, angled, glabrous(slightly rugose in fruit). Pappus of short barbellate bristles to -2mm long, white. Receptacle flat, with dense chaff. Chaff filiform, white, to 1cm long.

Flowering - July - September.

Habitat - Pastures, roadside ditches, low woods, streambanks.

Origin - Native to Europe.

Other info. - This is an unmistakable species in Missouri. The dense uncinate phyllaries of the involucre are an excellent characteristic for identification. The large basal leaves are usually withered by anthesis.
Don't get to close to the plant as the fruiting heads grab onto nearly everything.

Photographs taken at Geneva State Park, Geneva, Ohio, 8-4-00, and at Whirlpool State Park, Niagra Falls, NY., 8-6-00.


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