Trillium chloropetalum is a
perennial, clump-forming
herbaceous plant with a thick underground
rhizome. Like all trilliums, it has a
whorl of three
bracts (leaves) and a single
trimerous flower with 3
sepals, 3
petals, two whorls of 3
stamens each, and 3
carpels fused into a single
ovary with 3
stigmas.[7] Since its
flower has no stalk, T. chloropetalum belongs to
subgenus Sessilia, the sessile-flowered trilliums. It is one of the largest of all Trillium species, with a
scape (stem) from 20 to 70 cm (7.9 to 27.6 in) long. The bracts are broadly
ovate, 7 to 21 cm (2.8 to 8.3 in) long and 7 to 18 cm (2.8 to 7.1 in) wide, usually with brownish mottling but sometimes unmottled. Petal color is highly variable, typically ranging from pale greenish yellow to greenish bronze (or purplish green) to dark purple. A variety that lacks yellow pigments has petal colors ranging from white to reddish-purple. The flower petals enclose purple stamens, 15 to 30 mm (0.59 to 1.18 in) long, and a purple ovary. Flowering occurs from late February to early April.[4][8][9]
In the
San Francisco Bay Area, a white-petaled form of T. chloropetalum is often confused with
T. albidum, which also has white petals. The former is distinguished by the purple pigment in its anther
connective tissue, a character lacking in T. albidum.[10]
Taxonomy
In 1856,
John Torrey described Trillium sessile var. chloropetalum based on a specimen collected by
John Milton Bigelow two years earlier in the "redwoods" of California.[11][12] At the time, Bigelow was exploring the valleys and tributaries of the
Sacramento and
San Joaquin rivers, but the precise original location of his specimen remains unknown. In 1903,
Thomas Jefferson Howell described the species Trillium chloropetalum based on Torrey's variety.[13][14] The epithet chloropetalum means "green-petaled".[15]: 105
In 1975,
John Daniel Freeman published an influential revision of
subgenus Sessilia that included the description of a new species Trillium albidumJ.D.Freeman and a completely new circumscription of Trillium chloropetalum(Torr.) Howell.[16] By separating out white-flowered T. albidum, Freeman was able to provide a rational circumscription of T. chloropetalum that includes the following taxa:
Trillium chloropetalum var. chloropetalum
Trillium chloropetalum var. giganteum(Hook. & Arn.) Munz
The petals of T. chloropetalum var. chloropetalum always show yellow pigments but these are often masked by purple or other pigments.[17] In contrast, the petals of T. chloropetalum var. giganteum lack yellow pigments altogether.[18] The former is characterized by the green-petaled form described by Torrey while the latter includes a white-flowered form of T. chloropetalum distinguished from T. albidum by the presence of dark purple stamens and carpels.
Freeman's treatment of Trillium chloropetalum is widely (if not universally) accepted.[19][4][2][5] Some authorities consider Trillium chloropetalum var. giganteum to be a synonym for Trillium chloropetalum, but even those authorities cite Freeman.[8]
Distribution and habitat
Trillium chloropetalum is
endemic to
California. Some authorities claim the species ranges across ten California counties, from
Monterey County on the central California coast to
Lake County in the north central part of the state:[4][9]
Alameda, Contra Costa, Lake, Marin, Monterey, Napa, San Mateo, Santa Clara, Santa Cruz, Sonoma
^
abUSDA, NRCS (n.d.).
"Trillium chloropetalum". The PLANTS Database (plants.usda.gov). Greensboro, North Carolina: National Plant Data Team. Retrieved 7 March 2022.
^
ab"Trillium chloropetalum". Calflora. Berkeley, California: The Calflora Database. Retrieved 1 March 2022.
^"Trillium chloropetalum". County-level distribution map from the North American Plant Atlas (NAPA). Biota of North America Program (BONAP). 2014. Retrieved 27 February 2022.