genus
Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...
of
flowering plant
Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (). The term angiosperm is derived from the Ancient Greek, Greek words (; 'container, vessel') and (; 'seed'), meaning that the seeds are enclosed with ...
s in the
family
Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...
Cistaceae
The Cistaceae are a small family of plants (rock-rose or rock rose family) known for their beautiful shrubs, which are profusely covered by flowers at the time of blossom. This family consists of about 170(-200) species in eight genera that are ...
. They are native to both North and South America where they are widespread. The common name frostweed relates to the ice crystals which form from sap exuding from cracks near the base of the stem in the late fall.
''Crocanthemum'' are
herbaceous
Herbaceous plants are vascular plants that have no persistent woody stems above ground. This broad category of plants includes many perennials, and nearly all annuals and biennials.
Definitions of "herb" and "herbaceous"
The fourth edition of ...
perennial
In horticulture, the term perennial ('' per-'' + '' -ennial'', "through the year") is used to differentiate a plant from shorter-lived annuals and biennials. It has thus been defined as a plant that lives more than 2 years. The term is also ...
s or
subshrubs
A subshrub (Latin ''suffrutex'') or undershrub is either a small shrub (e.g. prostrate shrubs) or a perennial that is largely herbaceous but slightly woody plant, woody at the base (e.g. garden pink and florist's chrysanthemum). The term is ofte ...
with alternate leaves. With the exception of species in
California
California () is a U.S. state, state in the Western United States that lies on the West Coast of the United States, Pacific Coast. It borders Oregon to the north, Nevada and Arizona to the east, and shares Mexico–United States border, an ...
, they generally produce two types of flowers: showy, yellow chasmogamous (cross-pollinated) produced earlier in the growing season, followed by cleistogamous (self-pollinated) flowers that are smaller and lack petals. All species of ''Crocanthemum'' are fire tolerant and are found in open habitats.
Although the genus was first named in 1836 to encompass New World species of ''
Helianthemum
''Helianthemum'' (), known as rock rose, sunrose, rushrose, or frostweed,
'', it generally went unrecognized by taxonomists and its species were included in a broad concept of ''Helianthemum'' throughout much of the 1800s and 1900s. However, phylogenetic studies in 2004 and 2009 indicated that the New World species of ''Helianthemum'' were more closely related to '' Hudsonia'' than Old World ''Helianthemum''. This required the resurrection of the genus ''Crocanthemum'' in order to maintain monophyly.