Orthocarpus, commonly known as owl's-clover, is a genus of annual flowering plants in the family Orobanchaceae (the broomrape family), placed in the order Lamiales. The genus is native to North America and comprises around 9–11 accepted species. Plants are typically small, rarely exceeding 30 centimetres (about 1 foot) in height, with showy flower spikes that give them their "owl's-clover" common name — though they are not true clovers.
A defining biological trait of Orthocarpus is root hemiparasitism. Like their close relatives in the genus Castilleja (Indian paintbrush), Orthocarpus plants are capable of photosynthesis but supplement their nutrition by attaching to the roots of neighbouring host plants to extract water and minerals. This parasitic relationship means Orthocarpus species are closely tied to the presence of specific host plants in their grassland and meadow habitats.
The genus has historically been broader: a number of species once classified within Orthocarpus have been transferred to the genus Castilleja following molecular phylogenetic revisions. Orthocarpus plays a role in local ecosystems as a host plant for insects; the Edith's checkerspot butterfly (Euphydryas editha), for example, uses these plants as ovipositing hosts.
Etymology
The common name "owl's-clover" refers to the appearance of the flower spikes, which resemble owls' faces peering from the bracts. The scientific name Orthocarpus derives from Greek: orthos (straight) and karpos (fruit), referring to the straight capsule fruits of the genus.
Distribution
Orthocarpus species are native to North America, occurring primarily in western North America — from the Great Plains westward through the Rocky Mountains and Pacific Coast states and provinces. Species such as O. luteus extend across the northern Great Plains, while others like O. tenuifolius are found in montane meadows of the northwestern United States and adjacent Canada.
Ecology
Orthocarpus species are root hemiparasites that photosynthesize but also tap the roots of neighbouring grasses and forbs for water and mineral nutrients. They typically grow in open grasslands, meadows, and sagebrush steppe. The Edith's checkerspot butterfly (Euphydryas editha) uses Orthocarpus as a larval host plant, illustrating the genus's ecological role in supporting specialist insect communities.
Taxonomy Notes
Orthocarpus has been subject to significant taxonomic revision. Several species formerly placed in Orthocarpus have been transferred to the closely related genus Castilleja (Indian paintbrush) based on molecular phylogenetic evidence, reflecting the broader reorganisation of tribe Pedicularieae within Orobanchaceae. As of 2022, Plants of the World Online recognises around 9–10 accepted species in a more narrowly circumscribed Orthocarpus.
