Petrophyton cinerascens (orth. var. Petrophytum cinerascens) is a rare species of flowering plant in the rose family

Rosaceae

Rosaceae are a medium-sized family of flowering plants, including about 2830 species in 95 genera. The name is derived from the type genus Rosa. Among the largest genera are Alchemilla , Sorbus , Crataegus , Cotoneaster , and Rubus...

 known by the common names halfshrub rockmat and Chelan rockmat. It is endemic to the state of Washington in the United States, where it occurs in just a few locations along the Columbia River

Columbia River

The Columbia River is the largest river in the Pacific Northwest region of North America. The river rises in the Rocky Mountains of British Columbia, Canada, flows northwest and then south into the U.S. state of Washington, then turns west to form most of the border between Washington and the state...

 in Chelan and Douglas Counties.

This plant is a clumpy, mat-forming perennial herb growing in cracks and crevices in riverside cliffs. The stems are up to 30 centimeters long, arising from the mat of leaves. The stems bear raceme

Raceme

A raceme is a type of inflorescence that is unbranched and indeterminate and bears pedicellate flowers — flowers having short floral stalks called pedicels — along the axis. In botany, axis means a shoot, in this case one bearing the flowers. In a raceme, the oldest flowers are borne...

s 2 to 6 centimeters long of white flowers with many stamen

Stamen

The stamen is the pollen producing reproductive organ of a flower...

s. Blooming occurs in June through September.

There are five occurrences of this plant all in a 27-kilometer strech of cliffs along the Columbia River in central Washington. Two of the occurrences have about 1000 individuals each; the other three have fewer.

The plant is threatened by quarry

Quarry

A quarry is a type of open-pit mine from which rock or minerals are extracted. Quarries are generally used for extracting building materials, such as dimension stone, construction aggregate, riprap, sand, and gravel. They are often collocated with concrete and asphalt plants due to the requirement...

ing of rock nearby. Other threats include highway maintenance, introduced species

Introduced species

An introduced species — or neozoon, alien, exotic, non-indigenous, or non-native species, or simply an introduction, is a species living outside its indigenous or native distributional range, and has arrived in an ecosystem or plant community by human activity, either deliberate or accidental...

 of plants such as cheat grass

Drooping Brome

Drooping brome or Cheat Grass, Bromus tectorum, is a grass native to Europe, southwestern Asia and northern Africa.-Description:...

 (Bromus tectorum), herbicide

Herbicide

Herbicides, also commonly known as weedkillers, are pesticides used to kill unwanted plants. Selective herbicides kill specific targets while leaving the desired crop relatively unharmed. Some of these act by interfering with the growth of the weed and are often synthetic "imitations" of plant...

s, rock climbing

Rock climbing

Rock climbing also lightly called 'The Gravity Game', is a sport in which participants climb up, down or across natural rock formations or artificial rock walls. The goal is to reach the summit of a formation or the endpoint of a pre-defined route without falling...

, motor vehicle emissions

Motor vehicle emissions

Motor vehicle emissions are composed of the by-products that comes out of the exhaust systems or other emissions such as gasoline evaporation...

, and global warming

Global warming

Global warming refers to the rising average temperature of Earth's atmosphere and oceans and its projected continuation. In the last 100 years, Earth's average surface temperature increased by about with about two thirds of the increase occurring over just the last three decades...

.

External links

• Petrophytum cinerascens. Washington Burke Museum.
• USDA Plants Profile