Know Your Natives – Hairy Skullcap

Hairy skullcap (Scutellaria elliptica) of the Mint (Lamiaceae) family is one of nine skullcap species known to occur in Arkansas. The genus name is from the Latin scutella, a dish, in reference to the distinctive shape of the lower portion of the fruiting calyx (see below). The specific epithet refers to the leaf shape. The common name “skullcap” refers again to the unique form of the calyx, in particular the upper portion. This herbaceous perennial occurs in well-drained, sandy to rocky soils in partially sunny deciduous woodlands, woodland edges, and stream banks and terraces.  In Arkansas, it is only known to occur in the Interior Highlands.

Hairy skullcap, with a large number of slender, light tan, ropy roots, has a mature height of about 1 to 2 feet. New stems in late winter tend to be purple, but that color fades to a medium green with time. The plant, without runners or rhizomes, has up to a half-dozen erect square stems, with secondary, axillary stems arising along their upper portions. Main and axillary stems have terminal inflorescences. Axillary stems, in matched opposite pairs, are typically leafless except for leaves subtending the inflorescence. Stems are covered with dense short fine pubescence (tomentose), so that young stems appear fuzzy. As is true for all skullcaps, plants do not have a minty scent. Stems, although not woody, may persist over winter. Opposite leaf pairs are widely separated and decussate (adjoining pairs rotate 90 degrees).

Photo 1: Roots bear current-year and previous-year stems along with a bud for the next year. Inset: a tomentose stem and a pair of leaves (upper surface to left, lower to right).

Leaves below the inflorescence are up to 3 inches long and 1¾ inches wide, triangular-ovate, with scalloped margins (crenate). Leaf bases may be nearly straight (truncate) to rounded or slightly wedge-shaped (cuneate), with narrow strips of blade extending part way down the  petioles. Leaves, attached along the flat faces of the square stems, are a dark green above and a yellowish green beneath. Petioles, about ½ inch long, are rounded below and flattened to channeled above. In comparison with pubescence of the stems, that of the leaf blades is sparse, although longer and denser hairs occur along the primary and secondary vein below. Leaf margins are ciliate with short hairs.

Higher up the main stem, leaves that subtend axillary stems or flowers become gradually reduced, more elliptical, and with margins less crenate to entire. Also, petioles shorten and decurrent blade material may extend to the stem.

Photo 2: Opposite leaves are widely spaced on erect stems. A dead stem from the previous year remains at center-right. Photo – early April.
Photo 3: Upper leaves of the main stems subtend axillary stems or individual flowers. Leaf size and spacing decreases above. Photo – mid-May.

In mid to late spring, spike-like terminal racemes up to 4 inches long bloom over several weeks. Lower in the inflorescence, individual flowers are subtended by a leaf whereas higher flowers are subtended by small bracts (see below). Flowers, becoming more closely spaced up the raceme, are positioned in opposite decussate pairs. Sturdy, ⅛-inch-long pedicels, with two tiny basal bracts, extend out from the rachis at 45 degrees. Stems and rachises within the inflorescence have tomentose pubescence, becoming glandular on pedicels and calyxes.

Photo 4: Adaxial (left) and abaxial (right) surfaces of a leaf pair along with two racemes. Up-rachis, leaves become more elongate and less scalloped.

Flowers of all skullcaps have an oddly shaped calyx that becomes distinctively dish-shaped as fruits develop and the dorsal “skullcap” enlarges to become the prominent upper portion (see Photo 6 with both flowering and fruiting calyxes). With anthesis, a fist-shaped, closed corolla pushes out of the calyx, so that the skullcap is pushed backwards. The corolla’s tubular base bends sharply upward as the “fist” expands and opens. After the corolla drops off, the calyx again closes.

Corollas of hairy skullcap, about ¾ inch long, are elaborately bilabiate (two-lipped), with light blue to violet shades that fade into white accents. Lighter colors (often white) occur along the center of the lower lip and across the winged lobes of the upper lip. The upper lip is three-lobed: an upper lobe constricts to form a projecting, nearly-closed hood and two lateral lobes that “wing” outward. The lower lip has a broad, rather convex, notched central lobe and two down-flared lateral lobes. Flowers have two frontal orifices: the small upper orifice of the hood and the lower larger orifice formed by the two lips.

Flowers have four slender stamens and a slender style that are mostly hidden within the corolla tube and upper lip. Stamens, with their filaments fused to the lower portion of the corolla tube, occur as two pairs. The slender white filaments, with long hairs, bear two-lobed pubescent anthers that are positioned just inside the small orifice of the hood. The filaments surround a white style which extends from the four-lobed ovary to the opening of the hood. The small tapered stigma is slightly exserted. (When large bees land on the lower lip to collect nectar, the anthers are positioned to deposit pollen on the back of the bee or the stigma to collect pollen from the back of the bee.)

Photo 5: Base of tubular flowers bends sharply upward to an out-facing corolla. Anthers are hidden within the closed hood and stigma is slightly exserted from the hood.
Photo 6: Small bracts subtend flowers in upper portion of raceme. Flowers bloom sequentially from base to apex. Photo – mid-June.

Following anthesis, corollas quickly drop off. With fertilization, one to four ovules–one in each lobe of the four-lobed ovary–form seeds as the calyx enlarges to about ¼ inch. The fruit is a round, dark, one-seeded nutlet with numerous tiny wart-like tubercles across its surface. The calyx dries to a light tan color and the “skullcap” drops off so that nutlets may be dislodged by wind and rain. The “dish” section of the calyx remains on the dry plant into winter.

Photo 7: Display (a square = ¼ inch) showing the lower calyx section (on left – the dish section), the upper calyx section (on right – the skullcap section), and the tuberculate nutlets. (As shown, in reference to dish section, skullcap section is upside-down and reversed.) Photo – early September.

Hairy skullcap is appropriate for a partially shady garden or natural area with moist soils. This small- to medium-sized erect perennial herb has attractive foliage and beautiful, intriguing blue flowers. It does not have runners or rhizomes so that “extra” plants from self-seeding may be easily removed. Plants may be eaten by deer.

Nine species of skullcaps (one with three varieties) occur in Arkansas. They all have blue to violet flowers, but leaf shape can generally be used to distinguish hairy skullcap from the other eight species. A species with similar leaves is heart-leaf skullcap (Scutellaria ovata), but its leaf margins are more serrate and its adaxial leaf surface has a coarser appearance.

Species and varieties of skullcaps that occur in Arkansas:

  • Bush’s Skullcap (Scutellaria bushii)
  • Gulf Skullcap (Scutellaria cardiophylla)
  • Hairy Skullcap (Scutellaria elliptica)
  • Hoary Skullcap (Scutellaria incana)
  • Rough Skullcap (Scutellaria integrifolia)
  • Mad-Dog Skullcap (Scutellaria lateriflora)
  • Heart-Leaf Skullcap (Scutellaria ovata)
  • Southern Skullcap (Scutellaria parvula var. australis)
  • Glade Skullcap (Scutellaria parvula var. missouriensis)
  • Small Skullcap (Scutellaria parvula var. parvula)
  • South American Skullcap (Scutellaria racemosa) (non-native)

Article and photographs by ANPS member Sid Vogelpohl

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