Parnassiaceae

[2] When that system was published in 2009, Parnassiaceae were treated as subfamily Parnassioideae of an expanded family Celastraceae.

[5] Lepuropetalon has a disjunct distribution, being known from the southeastern United States and central Chile,[6] but is probably far more common than has been reported.

[7] Parnassia is a genus of perennial herbs, up to 60 cm tall, that grow in bogs, marshes, and other wet areas, mostly in cool to cold climates of the north temperate zone.

[12] Parnassiaceae are rhizomatous perennial herbs (Parnassia) or winter annuals without a rhizome (Lepuropetalon).

In both genera, the lower cauline leaves are pseudosessile,[4] which means that the petioles are adnate to the stems.

The inflorescence consists of one, or rarely two, flowers that face upward and are at the end of a peduncle that has few or no leaves.

In Parnassia, the petals are showy and white or cream, with conspicuous veins that are usually green or gray.

[3] The ovules are attached to T-shaped placentas in Parnassia, and directly to the ovary wall in Lepuropetalon.

The stigmas are decurrent along the commissures of the ovary and sometimes extended above, to form false styles called stylodia.

Such commissural stigmas have been discovered in Celastraceae,[13] but as late as 1972, they were known only from Parnassiaceae and from the basal eudicot family Papaveraceae.

[16] The name is from two Greek words, lepyron, "husk, rind, or shell", and petalon, "leaf or petal".

[17] In 1930, botanist Adolf Engler published descriptions of Lepuropetalon and Parnassia with detailed illustrations.

In 2005, a study of flower structure concluded that the family Parnassiaceae belonged in the order Celastrales with Lepidobotryaceae, and a broadly defined Celastraceae, including Mortonia and Pottingeria.

[13] In 2006, a study of DNA sequences confirmed that Lepuropetalon and Parnassia form a strongly supported clade.

[19] This study also showed strong support for a pentatomy consisting of Pottingeria, Mortonia, Parnassiaceae, and two clades of genera from Celastraceae as that family had been circumscribed in APG II.

In 2009, the Angiosperm Phylogeny Group expanded the family Celastraceae to consist of the five clades of the pentatomy mentioned above.