''Petrophytum caespitosum'' ( ''Petrophyton caespitosum'') is a woody perennial species of flowering plant in the

rose family Rosaceae (), the rose family, is a medium-sized family of flowering plants that includes 4,828 known species in 91 genera. The name is derived from the type genus ''Rosa''. Among the most species-rich genera are '' Alchemilla'' (270), ''Sorbus ...

known by the common name mat rock spiraea and native to western United States.

Range and Habitat

''Petrophytum caespitosum'' is native to the

Western United States The Western United States (also called the American West, the Far West, and the West) is the region comprising the westernmost states of the United States. As American settlement in the U.S. expanded westward, the meaning of the term ''the Wes ...

where it grows in mountainous areas from the

Sierra Nevada The Sierra Nevada () is a mountain range in the Western United States, between the Central Valley of California and the Great Basin. The vast majority of the range lies in the state of California, although the Carson Range spur lies primarily ...

to the

Rocky Mountains The Rocky Mountains, also known as the Rockies, are a major mountain range and the largest mountain system in North America. The Rocky Mountains stretch in straight-line distance from the northernmost part of western Canada, to New Mexico in ...

. It grows among limestone rocks in forested and woodland habitat and on open limestone bluffs and cliffs.

Description

''Petrophytum caespitosum'' is a very low matted

shrub A shrub (often also called a bush) is a small-to-medium-sized perennial woody plant. Unlike herbaceous plants, shrubs have persistent woody stems above the ground. Shrubs can be either deciduous or evergreen. They are distinguished from trees ...

growing in carpets up to 80 centimeters wide, creeping over rocks. The plant often grows on vertical surfaces and hangs by its roots, which cling to cracks in rock. The stems are thick and very short, covered densely in rosettes of oval leaves. Both surfaces of the leaves are lightly covered in short fine hairs, which may not be obvious without close inspection. It produces many

inflorescence An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Morphologically, it is the modified part of the shoot of seed plants where flowers are formed o ...

s which are spikelike clusters of flowers arising on erect peduncles up to 10 centimeters tall. Each inflorescence is packed with flowers, each with five tiny white petals, many whiskery

stamen The stamen (plural ''stamina'' or ''stamens'') is the pollen-producing reproductive organ of a flower. Collectively the stamens form the androecium., p. 10 Morphology and terminology A stamen typically consists of a stalk called the filame ...

s, and usually 5 hairy

pistils Gynoecium (; ) is most commonly used as a collective term for the parts of a flower that produce ovules and ultimately develop into the fruit and seeds. The gynoecium is the innermost whorl of a flower; it consists of (one or more) ''pistils'' ...

. The flower parts dry and may fall away, leaving a cluster of developing fruits, follicles containing the seeds.Southwest Colorado Wildflowers
/ref>

References

External links

Jepson Manual Treatment

Calphotos gallery
{{- caespitosum Flora of California Flora of the Northwestern United States Flora of the Southwestern United States Flora of Arizona Flora of New Mexico Flora of the Rocky Mountains Flora of the Sierra Nevada (United States) Flora of Texas Flora of the California desert regions Natural history of the Grand Canyon Natural history of the Mojave Desert Flora without expected TNC conservation status