Valeriana acutiloba and Valeriana occidentalis are very similar species and I have a difficult time separating them. Floras do agree that the corolla shape and size are key to distinguishing between the species, but the characteristics of the leaves and stems are not agreed on.

The "Flora of the Four Corners Region":
V. acutiloba: Basal leaves 3-14 cm long; corolla of perfect flowers funnelform, 5-9 mm long.
V. occidentalis: Basal leaves 10-25 cm long; corolla of perfect flowers rotate, 2-5 mm long.

"Flora of Colorado":
V. acutiloba: Corolla mostly 4-7 mm long, usually somewhat hairy outside near the base, the lobes to half as long as the tube; flowers usually all perfect; stem usually with minutely spreading hairs.
V. occidentalis: Corolla mostly 2-4 mm long, glabrous outside, the lobes nearly or as long as the tube; flowers often chiefly all pistillate; stem glabrous or nearly so.

"Flora Neomexicana III" and "A Utah Flora":
V. acutiloba: Corolla tube longer and funnelform, 4-6 mm long; leaves ovate to spatulate in outline, the lateral segments of the stem leaves usually narrowly lanceolate and acuminate.
V. occidentalis: Corolla tube short, the limb widely flaring (rotate or nearly so) , 2-3.5 mm long; leaves mostly oblong in outline, the lateral segments of the stem leaves commonly broadly lanceolate to elliptic, obtuse to acute.

"Colorado Flora":
V. acutiloba: Corolla funnel-shaped or trumpet-shaped, with a definite cylindric tube and usually swollen at the base on one side.
V. occidentalis: Corolla narrowly cup-shaped, without a definite cylindric tube and not noticeably swollen at the base.

I find plants that have funnelform corollas (V. acutiloba) that are very short, ~3mm (V. occidentalis). I will assume I am mistaken and keep observing the plant to better understand them. Photographs on this page are, therefore, labeled with my best estimate of their name.

"Valerian" refers either to a Roman Emperor or (more probably) to the Latin word for strength, "valere", referring to the belief in Valerian’s potency as a nerve tonic and relaxant.  "Capitata" (as in "decapitate") refers to the rounded "head-shaped" flower.

Linnaeus named this genus in 1753. Rydberg collected the first specimen of what we now call V. acutiloba in the Sangre de Cristo Mountains of Eastern Colorado around 1900 and named and described the species in 1901.  Frederick Meyer renamed the plant Valeriana capitata in 1951, but it has now reverted to Rydberg's original name. Heller collected V. occidentalis in Idaho and named and described it in 1898.

 Above left: Valeriana acutiloba. Synonym: Valeriana capitata subspecies acutiloba. (Valerian)
 Above right: Valeriana occidentalis (Western Valerian)
Caprifoliaceae. Synonym: Valerianaceae. (Honeysuckle Family)

Montane, subalpine. Meadows, openings. Summer.
Lower Stoner Mesa Trail, May 26, 2004 and
Meadow below El Diente, June 21, 2020.

These Valerians are slim plants with very conspicuous white-to-purple flower clusters balanced perfectly above thin stems.

Valerians are common early summer flowers and often are thickly scattered over small forest openings and meadows.

"Valerian" refers either to a Roman Emperor or (more probably) to the Latin word for strength, "valere", referring to the belief in Valerian’s potency as a nerve tonic and relaxant.  "Capitata" (as in "decapitate") refers to the rounded "head-shaped" flower and "acutiloba" refers to the tips of the corolla lobes.