Polycnemoideae
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| Polycnemoideae | |
|---|---|
 | |
| Nitrophila occidentalis | |
Scientific classification  | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Eudicots |
| Order: | Caryophyllales |
| Family: | Amaranthaceae |
| Subfamily: | Polycnemoideae Ulbr. |
| Genera | |
|
4 genera, see text | |
The Polycnemoideae are a small subfamily of plants in the family Amaranthaceae sensu lato.[1] The few relictual species are distributed in Eurasia and North Africa, North America, and Australia.
The subfamily Polycnemoideae comprises small herbs; some species are weakly lignified and grow shrublike. The subfamily is distinguishable from all other members of Amaranthaceae by normal secondary growth. The alternate or opposite leaves are often linear or subulate. The stomata of the leaves are arranged in parallel to the midveins.[2]
The bisexual flowers are sitting solitary in the axil of a bract and two bracteoles. The inconspicuous perianth is formed of chartaceous, scarious, white or pinkish tepals. One to five stamens are present with their filaments united in a short but distinct filament tube (like in subfamily Amaranthoideae). Anthers are with only one lobe and two pollen sacs (bilocular, like in subfamily Gomphrenoideae). In fruit, the tepals are never conspicuously modified.[2]
Photosynthesis pathway
Distribution and evolution
The Polycnemoideae are distributed in the temperate regions of Eurasia (central and southern Europe, northwestern Africa, Central Asia), North America, and Australia.[2]
Polycnemoideae began to diverge from Amaranthaceae sensu stricto in the Eocene.[citation needed] At the edge from Eocene to Oligocene, the subfamily split into a lineage in the Northern Hemisphere, which was the ancestor of Polycnemum, and a lineage predominantly occurring on the Southern Hemisphere with the ancestors of Nitrophila, Hemichroa, and Surreya.[citation needed] An Antarctic connection of these southern ancestors is assumed.[citation needed] The genus Nitrophila developed in South America and dispersed later to North America.[citation needed] The genera of the subfamily diversified during Miocene and Pliocene, with only a few rare species that seem to be relictual.[3]
