Wyoming Native Plants
Plant of the Month
| | Common Name: Rock Spiraea
Scientific Name: Petrophytum caespitosum | | |
If you go wandering amongst rocky hillslopes of our public lands, you may be lucky enough to encounter Rock Spirea or Rock mat (Petrophytum caespitosum). The leaves form short dense mats of basal rosettes covering the rocks, while white- pink flowers are clustered inches above the mat on racemes 1-2 inches tall. Rock mat flowers between June- September and you wouldn’t think it, but if you look closely at its flowers you can see clues that this strange little plant is actually a member of the rose family (Rosaceae).
Rock mat often grows on limestone, dolomite, or limey sandstone outcrops, with its rocky affinities captured in its Latin name, which literally translates to rock (petro) plant (phytum). The species name caespitosum refers to its mat-like form. It is native to the western United States, ranging from Oregon to Montana and south to California, Texas, and Northern Mexico.
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