Pleiacanthus
Encyclopedia
Pleiacanthus is a monotypic genus of flowering plants in the aster family
containing the single species Pleiacanthus spinosus (formerly Stephanomeria spinosa), which is known by the common name thorn skeletonweed, or thorny skeletonweed. It is native to the western United States from Montana
and Idaho
to southern California
and Arizona
, where it grows in many types of mostly dry habitat from deserts to mountains. It is a spindly subshrub
producing several slender stems up to 40 or 50 centimeters tall from a woody caudex
. The stems divide many times into short, rigid branches which narrow to sharp thorn-tips. The plant is mostly hairless except for brownish woolly tufts at the base and below the basal leaves. The leaves are small and linear on the lower stem, and reduced to scale-like growths on the upper branches. Flower heads
occur near the ends of the branches. Each has a cylindrical base wrapped in one layer of phyllaries
. The head contains 3 to 5 ray florets, each with an elongated tube and a pale to bright pink ligule. The fruit is an achene
tipped with a cluster of pappus bristles
which are not plumelike as are those of the Stephanomeria
species with which this plant was once classified.
Asteraceae
The Asteraceae or Compositae , is an exceedingly large and widespread family of vascular plants. The group has more than 22,750 currently accepted species, spread across 1620 genera and 12 subfamilies...
containing the single species Pleiacanthus spinosus (formerly Stephanomeria spinosa), which is known by the common name thorn skeletonweed, or thorny skeletonweed. It is native to the western United States from Montana
Montana
Montana is a state in the Western United States. The western third of Montana contains numerous mountain ranges. Smaller, "island ranges" are found in the central third of the state, for a total of 77 named ranges of the Rocky Mountains. This geographical fact is reflected in the state's name,...
and Idaho
Idaho
Idaho is a state in the Rocky Mountain area of the United States. The state's largest city and capital is Boise. Residents are called "Idahoans". Idaho was admitted to the Union on July 3, 1890, as the 43rd state....
to southern California
California
California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...
and Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
, where it grows in many types of mostly dry habitat from deserts to mountains. It is a spindly subshrub
Shrub
A shrub or bush is distinguished from a tree by its multiple stems and shorter height, usually under 5–6 m tall. A large number of plants may become either shrubs or trees, depending on the growing conditions they experience...
producing several slender stems up to 40 or 50 centimeters tall from a woody caudex
Caudex
A caudex is a form of stem morphology appearing as a thickened, short, perennial stem that is either underground or near ground level . It may be swollen for the purpose of water storage, especially in xerophytes...
. The stems divide many times into short, rigid branches which narrow to sharp thorn-tips. The plant is mostly hairless except for brownish woolly tufts at the base and below the basal leaves. The leaves are small and linear on the lower stem, and reduced to scale-like growths on the upper branches. Flower heads
Head (botany)
The capitulum is considered the most derived form of inflorescence. Flower heads found outside Asteraceae show lesser degrees of specialization....
occur near the ends of the branches. Each has a cylindrical base wrapped in one layer of phyllaries
Bract
In botany, a bract is a modified or specialized leaf, especially one associated with a reproductive structure such as a flower, inflorescence axis, or cone scale. Bracts are often different from foliage leaves. They may be smaller, larger, or of a different color, shape, or texture...
. The head contains 3 to 5 ray florets, each with an elongated tube and a pale to bright pink ligule. The fruit is an achene
Achene
An achene is a type of simple dry fruit produced by many species of flowering plants. Achenes are monocarpellate and indehiscent...
tipped with a cluster of pappus bristles
Pappus (flower structure)
The pappus is the modified calyx, the part of an individual disk, ray or ligule floret surrounding the base of the corolla, in flower heads of the plant family Asteraceae. The pappus may be composed of bristles , awns, scales, or may be absent. In some species, the pappus is too small to see...
which are not plumelike as are those of the Stephanomeria
Stephanomeria
Stephanomeria is a genus of plants also known as wirelettuce, belonging to the family Asteraceae. The ten perennial and six annual species are restricted to western North America....
species with which this plant was once classified.