''Rhexia'' is a genus of

flowering plant Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. The term "angiosperm" is derived from the Greek words ('container, vessel') and ('seed'), and refers to those plants th ...

s in the family

Melastomataceae Melastomataceae is a family of dicotyledonous flowering plants found mostly in the tropics (two-thirds of the genera are from the New World tropics) comprising c. 175 genera and c. 5115 known species. Melastomes are annual or perennial herbs, sh ...

. ''Rhexia'' species are commonly called "meadow beauty" and 11 to 13 species of ''Rhexia'' have been recognized depending on different taxonomic treatments.

Distribution

Unlike other members of the same family showing

pantropical A pantropical ("all tropics") distribution is one which covers Tropics, tropical regions of both hemispheres. Examples of species include caecilians, modern sirenians and the plant genera ''Acacia'' and ''Bacopa''. ''Neotropical'' is a zoogeogra ...

distribution, ''Rhexia'' is mainly distributed in temperate region of southeastern part of North America; from Nova Scotia to Florida and the West Indies (Cuba, Hispaniola, and Puerto Rico) and west to eastern Texas. The species of ''Rhexia'' are frequently found in wet meadows, coastal plain marshes, sandy wetlands and lake edges, pine woods, and road-side swales. Most ''Rhexia'' species successfully establish on open areas disturbed by recurrent burning or reclamation.

Description

''Rhexia'' species 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 t ...

perennials A perennial plant or simply perennial is a plant that lives more than two years. The term ('' per-'' + '' -ennial'', "through the years") is often used to differentiate a plant from shorter-lived annuals and biennials. The term is also widel ...

. Opposite leaves are simple, ovate to lanceolate and have the typical acrodromous venation (prominent arcuate nerves) characteristic of the

. Stems have four faces; one set is broader and convex, the other set is narrower, concave. Flowers are actinomorphic (radially symmetrical), 2–3 cm in diameter, pink-purple to white, (yellow in ''R. lutea''), petals 4, sepals 4, stamens 8. Bright yellow anthers are long and curved counterclockwise. Seeds are cochleate (noncochleate in ''R. alifanus'').

Pollination

The

is a large tropical plant family characterized by

buzz pollination Buzz pollination or sonication is a technique used by some bees, such as solitary bees to release pollen which is more or less firmly held by the anthers. The anthers of buzz-pollinated plant species are typically tubular, with an opening at onl ...

. Like other members of the family, it appears that flowers of ''Rhexia'' species are buzz pollinated. For example, ''Rhexia virginica'' is buzz pollinated by

bumblebee A bumblebee (or bumble bee, bumble-bee, or humble-bee) is any of over 250 species in the genus ''Bombus'', part of Apidae, one of the bee families. This genus is the only extant group in the tribe Bombini, though a few extinct related gener ...

s and shows two representative features of the buzz pollination syndrome; bright yellow anthers and flower color changes after

anthesis Anthesis is the period during which a flower is fully open and functional. It may also refer to the onset of that period. The onset of anthesis is spectacular in some species. In ''Banksia'' species, for example, anthesis involves the extension ...

Taxonomy

Taxonomic treatments of ''Rhexia'' suggested by James (1956) and Kral and Bostick (1969) have been broadly used. Both James (1956) and Kral and Bostick (1969) recognized two main groups (series A and series B) within ''Rhexia'' based on morphological characters of anthers. Species in series A have 2 mm long straight, ascending anthers and three species (''R. petiolata, R. nuttallii, and R. lutea'') belong to this group. Eight members of series B show 4–11 mm long descending, curved anthers (''R. alifanus, R. mariana, R. virginica, R. salicifolia, R. cubensis, R. aristosa, ''R. parviflora'' and R. nashii''). Recently, new infrageneric classification of ''Rhexia'' was suggested by Nesome (2012) based mainly on stem morphology. Nesom (2012) recognized 13 species within ''Rhexia'' by treating two tetraploid ''R. mariana'' var. ''ventricosa'' and ''R. mariana'' var. ''interior'' as specific rank based on allopatric distribution and distinct stem morphology of these entities. The Nesome's classification divides ''Rhexia'' into four sections: (1) Sect. RHEXIA (''R. aristosa, R. salicifolia, R. virginica, R. interior, R. ventricosa, R. mariana, R. cubensis, R. nashii, R. parviflora''; (2) Sect. CYMBORHEXIA (''R. alifanus''); (3) Sect. BREVIANTHERA (''R. petiolata, R. nuttallii''; and (4) Sect. LUTEORHEXIA (''R. lutea''). RhexiaLutea

Molecular phylogeny

Ionta ''et al''. (2007) reconstructed

phylogeny A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

of ''Rhexia'' species based on molecular data (nuclear ribosomal DNA and chloroplast DNA sequence) and morphological data. The analyses supported a

phylogenetic tree A phylogenetic tree (also phylogeny or evolutionary tree Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, MA.) is a branching diagram or a tree showing the evolutionary relationships among various biological spec ...

with three major

clades A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, t ...

: (1) ''R. petiolata'' clade (''R. alifanus, R. nuttallii, R. petiolata''); (2) ''R. mariana'' clade (''R. mariana''); and (3) ''R.virginica'' clade (''R.virginica, R. aristosa''). Remaining species showed incongruence between nuclear ribosomal DNA tree and chloroplast DNA tree (''R. lutea, R. nashii, R. salicifolia'') and/or multiple

alleles An allele (, ; ; modern formation from Greek ἄλλος ''állos'', "other") is a variation of the same sequence of nucleotides at the same place on a long DNA molecule, as described in leading textbooks on genetics and evolution. ::"The chro ...

of ncpGS (''R. cubensis, R. lutea, R. nashii, R. parviflora, and R. salicifolia'') implying putative hybrid origin of these species.

Species list

This infrageneric classification of ''Rhexia'' is based on Nesom (2012). Section RHEXIA • '' Rhexia aristosa'' Britton • ''

Rhexia salicifolia ''Rhexia'' is a genus of flowering plants in the family Melastomataceae. ''Rhexia'' species are commonly called "meadow beauty" and 11 to 13 species of ''Rhexia'' have been recognized depending on different taxonomic treatments. Distribution ...

'' Kral & Bostick • '' Rhexia virginica'' L. • ''

Rhexia mariana ''Rhexia mariana'' is a species of flowering plant in the Melastomataceae family known by the common names pale meadow beauty or Maryland meadowbeauty. It is native to the eastern and lower midwestern United States.Rhexia cubensis'' Griseb. • '' Rhexia nashii'' Small • '' Rhexia parviflora'' Chapm. Section CYMBORHEXIA • '' Rhexia alifanus'' Walter Section BREVIANTHERA • ''

Rhexia nuttallii ''Rhexia'' is a genus of flowering plants in the family Melastomataceae. ''Rhexia'' species are commonly called "meadow beauty" and 11 to 13 species of ''Rhexia'' have been recognized depending on different taxonomic treatments. Distribution ...

'' C.W. James • ''

Rhexia petiolata ''Rhexia'' is a genus of flowering plants in the family Melastomataceae. ''Rhexia'' species are commonly called "meadow beauty" and 11 to 13 species of ''Rhexia'' have been recognized depending on different taxonomic treatments. Distribution ...

'' Walter Section. LUTEORHEXIA • ''

Rhexia lutea ''Rhexia'' is a genus of flowering plants in the family Melastomataceae. ''Rhexia'' species are commonly called "meadow beauty" and 11 to 13 species of ''Rhexia'' have been recognized depending on different taxonomic treatments. Distribution ...

'' Walter

References

{{Taxonbar, from=Q7320496 Melastomataceae genera