Perideridia howellii

{{Short description|Species of flowering plant}}

{{Speciesbox

|image =

|genus = Perideridia

|species = howellii

|authority = (J.M.Coult. & Rose) Mathias

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Perideridia howellii is a species of flowering plant in the family Apiaceae known by the common name Howell's yampah.[https://plants.usda.gov/java/profile?symbol=PEHO5 USDA Plants Profile] It is native to the mountains of Oregon and northern California, where it grows in moist soils, often near streams and rivers.[http://ucjeps.berkeley.edu/cgi-bin/get_JM_treatment.pl?329,497,506 Jepson Manual Treatment] It is a perennial herb which may exceed 1.5 metres in maximum height, its slender, erect stem growing from a cluster of many narrow fibrous roots measuring up to 15 centimetres long. Leaves near the base of the plant have lance-shaped blades up to half a metre long which are divided into many leaflets made up of toothed, oval segments. Leaves higher on the plant are similar, but generally smaller. The inflorescence is a compound umbel of many spherical clusters of small white flowers. These yield ribbed, oblong-shaped fruits each about half a centimetre long.