Ptilimnium costatum Raf.

Big Mock Bishop's Weed


CC = 7
CW = -5
MOC = 17

© SRTurner

Family - Apiaceae

Habit - Annual forb.

Stem - Erect or ascending, to 1.5 m, glabrous.

Ptilimnium_costatum_stem.jpg Stem.

© SRTurner

Leaves - Alternate, petiolate with sheathing bases. Blades to 15 cm long, 2-3x pinnately dissected, with main segments mostly in whorls of 3-5 along the rachis, the ultimate divisions 3-18 mm long, threadlike.

Ptilimnium_costatum_leaf.jpg Leaf.

© SRTurner

Inflorescence - Compound umbels. Involucre of 4-15 bracts, these 5-12 mm long, narrowly linear, mostly entire. Rays 12-25, 1.5-4.5 cm long. Involucel of 2-5 bractlets, these shorter than the flower stalks, linear.

Ptilimnium_costatum_involucre.jpg Involucre.

© SRTurner

Ptilimnium_costatum_inflorescence1.jpg Inflorescence.

© SRTurner

Ptilimnium_costatum_inflorescence2.jpg Inflorescence, ventral view.

© SRTurner

Flowers - Florets 15 to numerous in each umbellet, on stalks 2-6 mm long. Sepals minute triangular scales. Petals obovate, often notched at tips, white.

Ptilimnium_costatum_florets.jpg Florets.

© SRTurner

Fruits - 2-4 mm long, glabrous, with relatively narrow, inconspicuous, dark brown surfaces between the lateral ribs and the commissures, and also between the ribs, the oil tubes inconspicuous.

Ptilimnium_costatum_fruits.jpg Fruits.

© SRTurner

Flowering - July - September.

Habitat - Swamps, sloughs, streambanks, acid seeps, ditches.

Origin - Native to the U.S.

Lookalikes - Several other members of the Apiaceae, e.g. those in the genera Angelica, Torilis, Ligusticum, and several others.

Other info. - At a sideways glance this plant may resemble Queen Anne's Lace; however, the leaves are totally different. The plant is relatively uncommon. In Missouri it is largely restricted to the Bootheel region. It is also found in several southeastern states, but nowhere is it common. The photos above represent a somewhat disjunct population, occurring in a wet powerline cut in Franklin County.

Photographs taken at Robertsville State Park, Franklin County, MO, 8-1-2015 (SRTurner).