Trillium

 ( Melanthiaceae Genera ) 

The Trillium genus has traditionally been divided into two Subgenus, Trillium subgenus Trillium and Trillium subgenus Phyllantherum, based on whether the flower is pedicellate or sessile. At the time, the former subgenus was considered to be the more primitive group. Based on molecular systematics, Trillium subgen.  Phyllantherum has been shown to be a Monophyly group, but its segregation renders the remaining Trillium subgen.  Trillium Paraphyly.

Trillium subgenus Phyllantherum was named by Constantine Samuel Rafinesque in 1820, but since he did not provide a description, the name was declared invalid in 2014. At that time, the correct name was thought to be Trillium subgen.  Sessilium, which was described by Rafinesque in 1830. However, that name was later found to be incorrect as well. , the correct name of the subgenus is Trillium subgen.  Sessilia Its type species is Trillium sessile

In 1819, Rafinesque described and named the genus Delostylis, and then placed Trillium stylosum (now a synonym for Trillium catesbaei ) into the new genus. Reversing himself a decade later, Rafinesque instead placed Trillium stylosum into a new subgenus Delostylium in 1830. Presumably Rafinesque had intended the subgeneric name to replace the earlier generic name, and so the correct name of the former is Trillium subgen.  Delostylis . Its type species is Trillium catesbaei. Historically, the subgenus has been known as the Catesbaei group. The word Delostylis means "with a small but conspicuous style".

Based on morphology and genetic analysis, a few taxa in genus Trillium have been segregated into other genera:

• Trillium rivale, first described in 1885, was segregated into genus Pseudotrillium in 2002. The name Pseudotrillium rivale is widely recognized.
• Trillium govanianum, first described in 1839, was segregated into genus Trillidium in 1850. However, the name Trillidium govanianum is not widely recognized.
• Trillium undulatum, first described in 1801, was segregated into genus Trillidium in 2018, but the name Trillidium undulatum is controversial and not widely recognized.

Phylogenetic analysis places Trillidium govanianum and Trillidium undulatum together in a clade with high support. However, since Trillium and Trillidium are both individually and collectively monophyletic, it is a matter of choice whether or not to recognize genus Trillidium.

Excluding the segregate taxa listed above, the remaining taxa separate into four clades with the following names:

• Trillium subgen.  Trillium
• Trillium subgen.  Callipetalon
• Trillium subgen.  Delostylis as
• Trillium subgen.  Sessilia as

Traditionally, Trillium subgen.  Trillium has included all pedicellate-flowered species (which is a paraphyletic group), but in 2022, the subgenus was circumscribed as a clade of fourteen (14) species. Its type species is Trillium erectum Historically, the subgenus has been known as the Erectum group.

Trillium subgen.  Callipetalon was described by Jayne A. Lampley and Edward E. Schilling in 2022. The word Callipetalon means "beautiful petal", a reference to "the famously beautiful flowers" of its type species, Trillium grandiflorum Historically, the subgenus has been known as the Grandiflorum group.

This leads to a four-part concept of Trillium that sharply contrasts with the traditional pedicellate vs. sessile dichotomy outlined previously.

• Trillium apetalon – Japan, Kuril Islands, E Russia (Sakhalin)
• Trillium camschatcense – NE China (Jilin), Japan, Korea, Kuril Islands, E Russia (Primorsky Krai, Khabarovsk Krai, Kamchatka Peninsula, Sakhalin)
• Trillium cernuum – Manitoba, New Brunswick, Newfoundland, Nova Scotia, Ontario, Prince Edward Island, Quebec, Saskatchewan; Connecticut, Delaware, Illinois, Indiana, Iowa, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Dakota, Ohio, Pennsylvania, Rhode Island, South Dakota, Vermont, Virginia, West Virginia, Wisconsin; Saint Pierre and Miquelon
• Trillium channellii – Japan (E Hokkaido)
• Trillium erectum – New Brunswick, Nova Scotia, Ontario, Quebec; Connecticut, Delaware, Georgia, Illinois, Indiana, Kentucky, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia
• Trillium flexipes – Ontario; Alabama, Arkansas, Delaware, Illinois, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Missouri, New York, Ohio, Pennsylvania, South Dakota, Tennessee, Virginia, West Virginia, Wisconsin
• Trillium × hagae ( Trillium camschatcense × Trillium tschonoskii) – Japan, E Russia (S Sakhalin)
• Trillium hibbersonii – British Columbia
• Trillium × komarovii ( Trillium camschatcense × unknown) – Japan, E Russia (Primorsky Krai)
• Trillium × miyabeanum ( Trillium apetalon × Trillium tschonoskii) – Japan
• Trillium rugelii – Alabama, Georgia, North Carolina, South Carolina, Tennessee
• Trillium simile – Georgia, North Carolina, Tennessee
• Trillium smallii – Japan, E Russia (S Sakhalin)
• Trillium sulcatum – Alabama, Georgia, Kentucky, North Carolina, Tennessee, Virginia, West Virginia
• Trillium taiwanense – E Taiwan
• Trillium tschonoskii – Bhutan, China (Anhui, Fujian, Gansu, Hubei, Shaanxi, Sichuan, Tibet Autonomous Region, Yunnan, Zhejiang), NE India (Sikkim), Japan, Korea, Kuril Islands, Myanmar, Russia (Sakhalin), Taiwan
• Trillium vaseyi – Alabama, Georgia, North Carolina, South Carolina, Tennessee
• Trillium × yezoense ( Trillium apetalon × Trillium camschatcense) – Japan

• Trillium crassifolium – Washington
• Trillium grandiflorum – Nova Scotia, Ontario, Quebec; Alabama, Connecticut, Delaware, District of Columbia, Georgia, Illinois, Indiana, Iowa, Kentucky, Maine, Maryland, Massachusetts, Michigan, Minnesota, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, South Carolina, Tennessee, Vermont, Virginia, West Virginia, Wisconsin
• Trillium nivale – Illinois, Indiana, Iowa, Kentucky, Maryland, Michigan, Minnesota, Missouri, Nebraska, Ohio, Pennsylvania, South Dakota, West Virginia, Wisconsin
• Trillium ovatum – Alberta, British Columbia; California, Colorado, Idaho, Montana, Oregon, Washington, Wyoming
• Trillium scouleri – Alberta, British Columbia; Colorado, Idaho, Montana, Washington, Wyoming

• Trillium catesbaei – Alabama, Georgia, North Carolina, South Carolina, Tennessee
• Trillium georgianum – Georgia
• Trillium persistens – Georgia, South Carolina
• Trillium pusillum – Alabama, Arkansas, Kentucky, Maryland, Mississippi, Missouri, North Carolina, Oklahoma, South Carolina, Tennessee, Virginia, West Virginia
• Trillium texanum – Arkansas, Louisiana, Texas

• Trillium albidum – California, Oregon, Washington
• Trillium angustipetalum – California
• Trillium chloropetalum – California
• Trillium cuneatum – Alabama, Georgia, Kentucky, Mississippi, North Carolina, South Carolina, Tennessee
• Trillium decipiens – Alabama, Florida, Georgia
• Trillium decumbens – Alabama, Georgia, Tennessee
• Trillium delicatum – Georgia
• Trillium discolor – Georgia, North Carolina, South Carolina
• Trillium foetidissimum – Louisiana, Mississippi
• Trillium gracile – Louisiana, Texas
• Trillium kurabayashii – California, Oregon
• Trillium lancifolium – Alabama, Florida, Georgia, South Carolina, Tennessee
• Trillium ludovicianum – Louisiana, Mississippi, Texas
• Trillium luteum – District of Columbia, Georgia, Kentucky, North Carolina, Tennessee
• Trillium maculatum – Alabama, Florida, Georgia, South Carolina
• Trillium oostingii – South Carolina
• Trillium petiolatum – Idaho, Oregon, Washington
• Trillium recurvatum – Alabama, Arkansas, Illinois, Indiana, Iowa, Kentucky, Louisiana, Michigan, Mississippi, Missouri, Ohio, Tennessee, Texas, Wisconsin
• Trillium reliquum – Georgia, South Carolina
• Trillium sessile – Alabama, Arkansas, District of Columbia, Illinois, Indiana, Kansas, Kentucky, Maryland, Michigan, Missouri, New York, North Carolina, Ohio, Oklahoma, Pennsylvania, Tennessee, Virginia, West Virginia
• Trillium stamineum – Alabama, Mississippi, Tennessee
• Trillium tennesseense – Tennessee
• Trillium underwoodii – Alabama, Florida, Georgia
• Trillium viride – Illinois, Missouri
• Trillium viridescens – Arkansas, Kansas, Missouri, Oklahoma, Texas

• Trillium govanianum – NE Afghanistan, Bhutan, China (Tibet Autonomous Region, Yunnan), N + NE India (Himachal Pradesh, Jammu and Kashmir, Sikkim, Uttarakhand), Nepal, N Pakistan
• Trillium undulatum – New Brunswick, Nova Scotia, Ontario, Prince Edward Island, Quebec; Connecticut, Georgia, Kentucky, Maine, Maryland, Massachusetts, Michigan, New Hampshire, New Jersey, New York, North Carolina, Ohio, Pennsylvania, Rhode Island, South Carolina, Tennessee, Vermont, Virginia, West Virginia

• Trillium parviflorum is an accepted name by some authorities while others regard this name as a synonym of Trillium albidum subsp. parviflorum .

The following taxa are of historical interest:

• Trillium rivale has been segregated to a Monotypic taxon genus as Pseudotrillium rivale .
• Trillium ×  crockerianum was originally described as a hybrid with parents Trillium ovatum and Trillium rivale, but since the latter is now a member of genus Pseudotrillium, the hybrid has become an undescribed intergeneric hybrid, and therefore its taxonomic placement is uncertain.