Know Your Natives – Carolina Larkspur

Carolina larkspur (Delphinium carolinianum subsp. carolinianum) of the Buttercup (Ranunculaceae) family has irregular (bilaterally symmetrical) springtime flowers that are typically deep blue. The genus name is based on a Greek word for “dolphin”, in reference to the shape of flower buds (when viewed from the side). The specific epithet is a reference to one of the Carolinas, presumably the site of the type collection, i.e., the collected specimen upon which the species is based. In the U.S., the species Carolina larkspur occurs from New Mexico to North Dakota, east to Wisconsin, Kentucky, and South Carolina, and south to the Gulf Coast. The typic subspecies discussed here occurs from northeastern Texas and Louisiana, north to Iowa and Illinois, and across the Southeastern states. In Arkansas, it occurs throughout much of the state except for low lying areas of the Mississippi Alluvial Plain and West Gulf Coastal Plain. Habitat preference is sunny to partially sunny, dry-mesic to dry sandy or rocky woodlands, glades, prairies and roadsides on various substrates. The species is also known as blue larkspur and wild larkspur.

Carolina larkspur is an herbaceous perennial. It has a ground-hugging rosette of basal leaves in mid-winter, flowers in early spring, and mature fruit in late spring, after which the plant becomes dormant. 

The plant has basal and stem (cauline) leaves that, in outline, have an overall round to triangular shape. Leaf blades are deeply, palmately cut into three primary lobes, a terminal lobe and two laterals, and may be 3+ inches long and wide. Leaves are medium green adaxially, with lighter colored primary veins, and a lighter yellowish green abaxially. Blade and petiole are finely short pubescent to glabrate. Petioles, slender with a widened base, are round in cross-section with a flattened adaxial side . Venation is recessed above and expressed below, with the lower midvein being channeled.

Lobes of the earliest basal leaves have a wedge-shaped base and a fan-like apex. As additional basal leaves grow, their lateral lobes become deeply incised (though not reaching the petiole) so that leaves appear to have five primary lobes. With subsequent new leaves, lobes become more subdivided and sinuses more incised, till ultimately the blades comprise narrow, finger-like lobes, resulting in a “skeletal” appearance. Regardless of the degree of subdivision, lobing retains a pattern-of-three. Basal leaves wither, in age sequence, as the inflorescence develops.

Photo 1: Trifoliate character of leaves is readily seen in older basal leaves. Degree of leaf incision increases with later leaves. Photo – late January.
Photo 2: Structure of basal leaves become increasingly complex; however, trifoliate character of leaf blade and lobes is maintained. Photo – early March.

Stem leaves are widely spaced from stem base to immediately below the inflorescence, where they are replaced with bracts (see below). Leaves are arranged alternately, with lower stem leaves similar to the upper basal leaves. Leaves at the stem base have slender petioles to 6+ inches long; petioles are shorter about mid-stem and absent (leaves sessile) just below the inflorescence. Up-stem, both the size of the leaf blades and the complexity of their lobing decrease. Leaf coloration and venation are the same as that of basal leaves.

Photo 3: As the floral stem develops, the earliest wider-lobed basal leaves have withered. Remaining leaves have a “skeletal” appearance. Lowermost stem-leaves have especially long petioles with widened bases. Photo – late March.

Main stems, to about four feet tall, are erect, straight, terete and, typically, have downy pubescence (puberulent). (A shorter larkspur species that has similar basal leaves and blue flowers is dwarf larkspur, Delphinium tricorne.) Main stems support a raceme that may be a foot or more long. More robust plants may have shorter secondary stems growing from leaf axils at about 45 degrees that support shorter secondary racemes. Flowering proceeds from base to apex with fruits (capsules) already maturing at base as upper flowers continue to bloom. Flowers are each directly subtended by a pair of small opposite, linear bracts.

Photo 4: This robust plant is developing secondary stems at leaf axils along upper portion of main stem. Leaf size and degree of lobing decrease up-stem. Blooms of a much shorter dwarf larkspur can be seen in background. Photo – mid April.
Photo 5: A natural stand of Carolina larkspur in a sunny, rocky glade. Stem at left-foreground bears seed capsules, as upper flowers continue to bloom. Photo – Mid May.

Larkspurs are among the showiest of our native wildflowers. Close examination reveals that it is the petaloid sepals, rather than the petals themselves, that create the main attraction. Flowers, measuring about 1½ inches long and an inch wide, are typically a deep blue, but may be purplish or white. The symmetry is bilateral, described technically as irregular or zygomorphic, with one sepal of the dominant calyx positioned above the flower center and two sepals to either side. From the front of the flower (bee’s eye view), all sepals look the same, broad with a rounded apex and a distinct indentation on the face that corresponds with a green protrusion on the back. However, when viewed from the side, a half-inch-long, up-curved elongate, conical spur extends from the back of the upper sepal. 

Flowers also have four irregular petals that are significantly smaller than the sepals and are generally the same color, but petals may have various markings and color shadings. A matched pair of upper petals is very dissimilar to a matched pair of lower petals. While the sepals are thin in texture, the petals are thickened. The upper petals have an exserted up-flaring triangular portion with larger semi-tubular spurs that extend backward and are enclosed within the spur of the upper sepal.  This complex, compound tube serves as the nectary.

Lower petals, trending downward, are distally broad, rounded, and v-notched. Their outer surface bears long white twisty hairs, especially centered along the notches.

Stamens, pistils and ovaries are hidden below the lower pair of petals, although anthers may be partially visible. Three elongate, stubby whitish ovaries, fused to one another, directly above the pedicel, are in close contact with a number of stamens. Ovaries have stubby tapered styles tipped with the stigmas. Stamens have white flattened twisty filaments and dark elongate anthers.

Photo 6: Five sepals dominate the flowers’ appearance. Four irregular petals are grouped at center. Reproductive parts of flowers are mostly hidden by the two lower petals. Photo – late April.
Photo 7: A larkspur flower exploded to show parts (not Carolina larkspur). #1 – pedicel with pair of bracts. #2 – lower pairs of sepals. #3 – Upper sepal with partial spur; arrows indicate points of attachment. #4 – Upper pair of petals;  arrows indicate point of attachment (note semi-tubular shape with closed distal end). #5 – lower pair of petals. #6 – stamens. #7 – pistils (two of three shown).

The fruit of a fertilized flower comprises three slender, erect, dull-green follicles that are ½ to 1  inch long and fused together below to form a kind of three-parted capsule. The base of the capsule has a raised ring (calyx scar). Follicles are beaked with remnants of their  styles. When dry, the tannish papery follicles split, each along an inward suture at the upper end. Seeds drop free through the opened sutures or when follicles disintegrate. Tannish seeds have roughened, rounded and flattened surfaces.

Carolina larkspurs do well in rocky, sunny sites where soils are well drained. In a garden setting or natural area, mid-winter basal growth provides early greenery. Later stems provide early height to a garden, and blue flowers add dramatic impact, either singly or in groups. Larkspurs are attractive to various bees, including bumblebees, which often take the nectar by piercing the spur. An infestation of aphids can wipe out the inflorescence. Delphiniums are known to be toxic to humans and mammals. 

Two other subspecies of Carolina larkspur grow in Arkansas, both uncommon in the state: pinewoods larkspur (D. carolinianum subsp. vimineum) and plains larkspur (D. carolinianum subsp. virescens). Both are known in Arkansas only from the southwestern portion of the state. In comparison to Carolina larkspur, pinewoods larkspur has fewer, larger leaves with longer petioles and each with three primary, wider divisions. It occurs in sandy soils and is restricted to the Coastal Plain, ranging primarily in south-central and eastern Texas and western Louisiana. Plains larkspur also has fewer leaves with longer petioles, and white to light blue flowers.  It grows throughout the Great Plains, especially in prairies.  Both retain their basal leaves while the plants are in bloom, in comparison to the typic subspecies.

In addition to dwarf larkspur (D. tricorne, noted above), two other species are found in the state, namely, Moore’s delphinium (D. newtonianum) and Trelease’s larkspur (D. treleasei), both of very limited distribution in north (and west-central = Moore’s) Arkansas. Moore’s delphinium grows in moister, shaded sites and has less divided stem leaves and more diffuse inflorescences that bloom from apexes to the bases.  Trelease’s larkspur has flowers on long pedicels and grows exclusively in dolomite (a calcareous type) glades in the central Ozarks Highlands.

Article and photographs by ANPS member Sid Vogelpohl

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