Petrophytum caespitosum

Petrophytum caespitosum (Nutt.) Rydb.

by Laura Davis, Native Plants Class 2002
Common name: Rockmat, Rocky Mountain rockmat, tufted rockmat
Family: Rosaceae
Synonymy: Spiraea caespitosa, Eriogynia ceaspitosa
Etymology: Petrophytum caespitosum is aptly named as petros is the Greek word for rock and phyton is the Greek word for plant (5), and the epithet, caespitosum , refers to its mat like form (2).

Identification
Growth form: Petrophytum caespitosum is a mat-forming sub shrub which may grow 3' wide (2).
Roots: The root is stout and attaches to/in rock crevices (2).
Stem: The stems grow horizontally forming mats over limestone rocks (3).
Leaves: It has grayish green spatula or inversely lance-shaped leaves with silky hairs; in basal rosettes (1,2).
Inflorescences/flowers: The flowers are small, white to light pink with five petals, long stamens which are arranged in dense clusters on spike like raceme (1,2 )
Fruit: "Follicles about 1/12 in. long, 3-5, leathery, dehiscent on both sutures: seeds 2-4, linear" (5)
Similar species: The variety Petrophytum caespitosum var. elatoir has longer peduncles frequently branched and longer inflorescential bracts (5).

Ecology
Life history: Rockmat is a woody-tufted perennial (5).
Native/introduced: Native
Phenology: Flowers June to August (4).
Photosynthetic pathway:
Distribution: Petrophytum caespitosum is found "almost exclusively in hospitable habitat of barren rock" (4), in limestone rock crevices (5) and hanging gardens (2) between 3000-9500 ft, in Arizona, western Texas and New Mexico (5), northwestern Oregon, southern California, east to Montana, Colorado (4), and Mount Charleston, Nevada (personal observation).

Uses

References
1. Epple, A.O. and L.E. Epple, 1995. A Field Guide to the Plants of Arizona, Falcon Publishing Co., Helena, Montana.

2. Fagan, D., 1998. Canyon Country Wildflowers, A Field Guide to Common Wildflowers, Shrubs, and Trees, Falcon Publishing Co., Helena, Montana.

3. Hogan, P. and K. Huisinga, 1999. An Annotated Catalog of the Native and Naturalized Flora of Arizona, Arizona Ethnobotanical Research Association, Flagstaff, Arizona.

4. Spellenberg, R.,1986. The Audubon Society Field Guide to North American Wildfloers, Western Region, Alfred A Knopf, New York.

5. Vines,R.A., 1960. Trees, Shrubs and Woody Vines of the Southwest, University of Texas Press, Austin.

Petrophytum caespitosum (Nutt.) Rydb. by Laura Davis, Native Plants Class 2002 Common name: Rockmat, Rocky Mountain rockmat, tufted rockmat Family: Rosaceae Synonymy: Spiraea caespitosa, Eriogynia ceaspitosa Etymology: Petrophytum caespitosum is aptly named as petros is the Greek word for rock and phyton is the Greek word for plant (5), and the epithet, caespitosum , refers to its mat like form (2). Identification Growth form: Petrophytum caespitosum is a mat-forming sub shrub which may grow 3' wide (2). Roots: The root is stout and attaches to/in rock crevices (2). Stem: The stems grow horizontally forming mats over limestone rocks (3). Leaves: It has grayish green spatula or inversely lance-shaped leaves with silky hairs; in basal rosettes (1,2). Inflorescences/flowers: The flowers are small, white to light pink with five petals, long stamens which are arranged in dense clusters on spike like raceme (1,2 ) Fruit: "Follicles about 1/12 in. long, 3-5, leathery, dehiscent on both sutures: seeds 2-4, linear" (5) Similar species: The variety Petrophytum caespitosum var. elatoir has longer peduncles frequently branched and longer inflorescential bracts (5). Ecology Life history: Rockmat is a woody-tufted perennial (5). Native/introduced: Native Phenology: Flowers June to August (4). Photosynthetic pathway: Distribution: Petrophytum caespitosum is found "almost exclusively in hospitable habitat of barren rock" (4), in limestone rock crevices (5) and hanging gardens (2) between 3000-9500 ft, in Arizona, western Texas and New Mexico (5), northwestern Oregon, southern California, east to Montana, Colorado (4), and Mount Charleston, Nevada (personal observation). Uses References 1. Epple, A.O. and L.E. Epple, 1995. A Field Guide to the Plants of Arizona, Falcon Publishing Co., Helena, Montana. 2. Fagan, D., 1998. Canyon Country Wildflowers, A Field Guide to Common Wildflowers, Shrubs, and Trees, Falcon Publishing Co., Helena, Montana. 3. Hogan, P. and K. Huisinga, 1999. An Annotated Catalog of the Native and Naturalized Flora of Arizona, Arizona Ethnobotanical Research Association, Flagstaff, Arizona. 4. Spellenberg, R.,1986. The Audubon Society Field Guide to North American Wildfloers, Western Region, Alfred A Knopf, New York. 5. Vines,R.A., 1960. Trees, Shrubs and Woody Vines of the Southwest, University of Texas Press, Austin.


	© Charles A. Washburn © Charles A. Washburn