Astragalus sparsiflorus, the Front Range milkvetch, is a rare species of plant that grows in the Front Range mountains in Colorado.
Description
Front Range milkvetch is a low growing annual or short-lived perennial plant with a narrow taproot. It stems grow long and are either or decumbent, trailing along the ground or on the ground with the ends growing upwards, with small, sparse hairs that all point in the same direction.
Its compound leaves are long with 9 to 19 leaflets. The leaflets are obovate, oblong-oblanceolate, obcordate, almost orbiculate, or elliptic with a length of just 2–15 millimeters. Lower leaf surfaces are similarly hairy to the stems, sparsely strigilose, while the upper surfaces are hairless.
The flowers are white with an upper petal that has pink veins. They are arranged in a raceme, usually with 2 to 20 flowers, but that might have just one solitary bloom. Both varieties can bloom as early as May or as late as July, but variety sparsiflorus is known to bloom in August as well.
Taxonomy In 1863 the botanist Asa Gray described a new species of plant that he named Astragalus sparsiflorus. It is part of the genus Astragalus which is classified in the Fabaceae family and has two accepted varieties.
Astragalus sparsiflorus var. majusculus Variety majusculus was also described by Asa Gray, but in 1864. It grows along the South Platte River for about upstream from Denver.
Astragalus sparsiflorus var. sparsiflorus The autonymic variety of the species has no botanical synonyms. It grows in the mountains of eastern Colorado from the upper parts of the Arkansas River northward to the foothills of Pikes Peak and the upper reaches of the South Platte River.
It has five synonyms, three of the species and two of variety majusculus.
Table of Synonyms Name Year Synonym of: Notes Batidophaca sparsiflora 1929 A. sparsiflorus ≡ hom. Batidophaca variegata 1929 var. majusculus = het. Tium sparsiflorum 1905 A. sparsiflorus ≡ hom. Tium variegatum 1907 var. majusculus = het. Tragacantha sparsiflora 1891 A. sparsiflorus ≡ hom. Notes: ≡ homotypic synonym; = heterotypic synonym
Names Astragalus sparsiflorus is known by the common name Front Range milkvetch.
Range and habitat Front Range milkvetch is a Colorado endemic that grows mostly east of the Continental Divide in Custer, Fremont, El Paso, Teller, Park, Douglas, Jefferson, Denver, and Boulder counties. It grows west of the divide in just Grand County.
The species seems to require light amounts of natural soil disturbance to aid in reproduction.
Conservation In 2010 the IUCN rated the species as least concern on the IUCN Red List, however in 2025 NatureServe rated it as imperiled. NatureServe reports that of the 28 documented populations, less than half had been observed in the previous two decades. Along with its limited range it is impacted by competition from invasive species, recreation, development, fires, and fire fighting activities. Drought and climate change are also changing its natural habitat.
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