Tall bluebells is an herb in the borage family (Boraginaceae) with drooping blue bell-flowers and large ovate leaves. Tall bluebells is a common species across the park, found in floodplains, meadows and open forest in the boreal zone extending into subalpine meadows and shrublands and occasionally in tundra. Mertensia paniculata grows 20-60 cm tall from a short caudex or rhizome. The stem has many leaves, and plant usually has a few are basal leaves (sometimes the only structure to emerge in a given year is a cluster of basal leaves). Leaves are long ovate with acute tips, up to 15 cm long, deeply impressed with a branching network of veins. The leaves have stiff white hairs. The lower leaves have long petioles; the upper leaves are short-petioled or sessile. At the top of the stem, plants produce open panicles of flowers (the source of the scientific name 'paniculata')—a loosely branched inflorescence, with each branch bearing a row of flowers. The heads are nodding, with a short calyx and a much longer, narrow bell for the petals (10-20 mm long). Both the flower stems and sepals are covered in white hairs. The tube is constricted at the base, broadening, and with five short lobes at the tip. In bud, the petals are pink, becoming blue. Fruits are four nutlets per flower, all attached at the center, each with a single seed. No other plant in Denali has similar panicles of drooping blue bell flowers.
Tall bluebells is relatively early flowering. The flowers in a panicle mature sequentially. The young flowers produce pollen, older flowers produce nectar. Bees often rob flowers of their nectar by chewing through the side of the corolla (Morris 1996). However nectar robbery does not appear to reduce fertility of flowers—bees will gather pollen from younger flowers of the same inflorescence. hypothesizes that the benefit of older flowers attracting pollinators outweighs the cost of producing nectar.
Mertensia paniculata is endemic to North America, where it occurs across Canada and into the upper Great Lakes states and the Pacific Northwest in the U.S., including Montana. In Alaska, this species is common and widespread south of the Brooks Range, and north of the Alaska Peninsula and (apparently) absent from the southeast panhandle. Mertensia is widespread in suitable habitat across boreal to lower alpine regions of the park, including on both sides of the Alaska Range.
Although typically thought of as a lowland forest understory and meadow species, tall bluebells is most common in the alpine and subalpine of Denali. The average elevation where this species occurs in the Park is 788 meters, but reaches its highest level of cover and highest frequency at 900-1100 meters. It has a slight preference for southern aspects. Found on all degrees of incline, it grows most abundantly on moderate slopes.