Pinguicula macroceras, the California butterwort[1] or horned butterwort, is a species of perennial carnivorous herb that is native to the North American Pacific coast, as well as other select distributions in Canada, Russia, Japan, and the United States.

[3] With simple fleshy leaves (green-dark brown) that form a basal rosette, that are often recognized as slimy or sticky, and occasionally incurving over trapped prey.

[3] The corolla measures 13–21 mm with a lip that is often found to be hairy and generally does not block the throat of the flower.

[3] Moist slopes and serpentine banks along creeks and rivers, at an altitude less than 1800 m are places where they are likely to be located.

[4] Serpentine cliff sides (most often north facing) with fast flowing seeps have also been documented habitat of the Pinguicula macroceras.

[4] Moist habitats that are home to Pinguicula macroceras are often dominated by layers of moss that they form basal rosettes on top of and bury their roots underneath.

In North America P. macroseras is found within 750 km of the Pacific coast in California, Oregon, Washington, and into Canada.

[2] Pinguicula macroceras exists in an ecological niche that is unsuitable for most other types of plant life with some exceptions e.g. moss.

[4] The original specimens collected by Link were stored in Berlin and destroyed during World War II.

[4] Surviving specimens collected in 1933 by several other botanists from the same locations documented by Link were noted to have shorter spurs and named P.

[4] In 1968, Casper asserted that P. microceras was not a species or sub-species, and demonstrated that P. macroceras grown in harsher conditions will develop a reduced spur.

[6] The debate continues today between the two camps on whether P. macroceras is morphologically distinct enough from P. vulgaris to be considered a species.