Know Your Natives – Ouachita Hedge-Nettle

Ouachita Hedge-Nettle (Stachys iltisii*) of the Mint (Lamiaceae) family is a clonal herbaceous perennial with a spike-like inflorescence of two-lipped, white flowers with prominent purple blotches. The genus name is from the Greek for “an ear of wheat” in reference to the spike-like inflorescence. The specific epithet honors botanist Hugh Iltis. In the U.S., Ouachita Hedge-Nettle occurs in the Ouachita Mountains of Arkansas and Oklahoma along with scattered sites in the Arkansas Valley and Boston Mountains. Habitat preference is mesic deciduous woodlands.

Photo 1:  A low-lying woodland provides a preferred habitat for an expanding colony of Ouachita Hedge-Nettle. Photo – June 8.

Plants initially consist of a single stem, rhizomes (underground stems, here typically branching), and fibrous roots. During the growing season, a plant produces one to several rhizomes to a foot long. Young rhizomes are slender and round, but they become four-sided and ultimately develop an enlarged distal end from which, in spring, a single new upright stem rises.  At the end of the growing season, the initial plant dies, leaving one to a half dozen new rhizomes to produce a “disjointed” clonal colony. Rhizomes are white while the fibrous roots are white to tan. The four-sided stems may be hollow or filled with pith (a soft tissue), thus easily disintegrating before the next growing season.

Photo 2:  In display:  1) a dead stem from the previous year, 2) current-year stem with an ⅛ inch base, 3) the cut-off end of a four-sided, hollow parent rhizome, 4) a second current-year stem from the same parent rhizome (gap in rhizome), and 5) two disconnected growing rhizomes (tips to left)––rhizomes twisty due to rocky soil.  Photo June 13.  

Undamaged stems grow erect and unbranched to 3+ feet tall, clothed in spreading to reflexed long white hairs. Spring-time stems look and feel fuzzy while stems at the time of bloom are coarse and feel bristly. Non-flowering stems terminate with a pair of opposite leaves; flowering stems have a terminal spike-like inflorescence. Plants do not have basal leaves.

Photo 3:  Single new stems grow from the “tip” of a rhizome. The petiolate leaves and the four-sided stems have dense pubescence. Photo – March 30.

The simple leaves, in opposite, short-petiolate, decussate pairs (rotated 90⁰), are broadly lanceolate-elliptic with a rounded to truncate or lobed base and an acuminate tip. Largest leaves occur at about mid-stem to 7 inches long, 2½ inches wide, with up to a ¼ inch petiole. Uppermost leaves may be 1¼ inch long and ¼ inch wide with rounded, subsessile bases. Margins are serrate. Prominent pinnate venation is strongly recessed on the upper surface and strongly expressed on the lower surface. The reticulate pattern of tertiary veins is also prominent. The dull upper blade surface is densely pubescent with long reflexed hairs throughout. Hairs of the lower blade surface are significantly shorter. Both surfaces feel fuzzy. Except for the structural support provided by the veins, leaf blades are thin and flimsy.

Photo 4:  The opposite decussate leaf pairs are widely spaced and held nearly horizontal. Leaves are broadly lanceolate-elliptic with short petioles to subsessile. Photo – May 25.
Photo 5:  Display shows lower, mid, and uppermost leaves (upper and lower sides alternating). Leaves of lower pair are 6 inches long and 2½ inches wide, on a stem < 1/16 inch wide (in this case, hollow stems filled with pith). Leaves have pinnate venation and uniformly serrated leaf margins. Photo – June 5.

The spike-like inflorescence comprises a vertical series of densely packed whorls of cymose flower clusters (cymules), with 10-16 flowers per cluster**. The lowermost whorl tends to be subtended by the uppermost pair of stem leaves, the more distil whorls by pairs of greatly reduced bracts. Separation of whorls along the square-stemmed rachis varies from ¾ inch to ¼ inch, the greatest separation being between two lowermost whorls and gradually decreasing upwards. An inflorescence may have 10-16 whorls, to ½ inch wide and ¼ inch tall. Flowering sequence is typically from base to apex and, within each cymule, from the central flower to the laterals.

Photo 6:  Upper surfaces of leaves are convex and densely pubescent. Lower surfaces are less pubescent. Leaves extend into the inflorescence as subtending bracts that are pressed tightly against the whorls of cymules. Photo – May 10.
Photo 7:  Flowers are arranged in tight clusters comprising very stubby cymules. Central flower of a cymule blooms first, followed by lateral flowers. Flowers are favored by small bees and other insects. Photo –  May 25.

Flower corollas are two-lipped or bilabiate. The ascending upper lip is hooded, often with a central notch. The lower lip, extending downward, has a broad central lobe and a pair of  smaller rounded lateral lobes. Corollas are ⅜ inch long, base to tip. In bee’s eye view, they are ⅜ inch high with a landing pad, the lower lip, 3/16 inch wide, in color, white to pale lavender with prominent purple splotches on the lower lobe. Short glandular hairs cover the exterior of the flower. The ¼ inch long pubescent calyx has 5 triangular 1/16-inch-long pointed lobes.

Photo 8:  Whorl at lower right is positioned to show the top while the other three are positioned to show the bottom and their opposite pairs of bracts (see arrows). The pubescent campanulate calyxes have 5 triangular lobes. Photo – June 12.

Flowers have 4 stamens (filament + anther) and a single pistil (4-lobed ovary + style + stigma). Stamens are epipetalous––fused below to the corolla tube––with filaments bent so that the anthers are firmly fixed just below the hooded upper lip. The dark brown-purple anthers bear white pollen. The straight white style, tipped with a tiny 2-forked pointed stigma, arises from a deep notch between the ovary lobes. Filaments and style are about 7/16 inch long. Upper portion of filaments is covered with short glandular hairs. 

Photo 9:  Flower shown out of position with lower lobe on right, upper lobe on left. At their upper end, filaments bend sharply to direct the two-celled anthers (dark color) down onto entering insects. Forked stigma can be seen below anthers.  

With fertilization, the lobes of the ovary quickly develop into 4 one-seeded nutlets. These become 1/16 inch long and dark brown at maturity with minute irregular protrusions (tuberculate). They drop free with calyx movement.

Photo 10:  This post-bloom 6-inch long inflorescence segment has 15 whorls, each with two cymules bearing 5 to 8 calyxes. The 1/8-inch-long nutlets, at right, are tuberculate. Photo – July 27.  

For an informal garden or natural area, Ouachita Hedge-Nettle, with its well-spaced matching leaf pairs and spiky inflorescence, is structurally pleasing, probably best in a dedicated space with room to roam. In some settings, it may become aggressive. When deer nip off spring-time stems, a replacement pair of axillary stems tends to grow. Plants do not seem to be eaten by deer later in season. Like many 2-lipped-flowered mints, Ouachita Hedge-Nettle is a favorite nectar source for small bees and other insects.

In addition to Ouachita Hedge-Nettle, three other species of the genus are known to occur in Arkansas: Shade Betony (Stachys crenata), perhaps native to extreme southwest Arkansas, the non-native Florida Betony (S. floridana), and Smooth Hedge-Nettle (S. tenuifolia). Of these, Smooth Hedge-Nettle is the most similar, but it is a smaller, mostly glabrous plant with narrower, longer-petiolate leaves and calyxes with longer and reflexing lobes. It tends to grow in wetter sites and throughout the state. American Germander (Teucrium canadense), with similar habit and spike-like inflorescence, may be confused with Ouachita Hedge-Nettle (see Photo 11), however the corollas, with no upper hooded lip, distinguish it at once.

Photo 11:  Ouachita Hedge-Nettle (left), as compared to American Germander (right), generally does not branch, blooms earlier, and has short petiolate fuzzy leaves. Photo – June 5. Inset: inflorescence of American Germander, showing with corollas lacking a hooded upper lip.

*  Before being described as a new species in 2008, Ouachita Hedge-Nettle was known as Epling’s Hedge-Nettle (Stachys eplingii). As now understood, Epling’s Hedge-Nettle occurs in widely scattered sites between Alabama and Virginia.

** Plants with fewer than expected flowers per cymule are found scattered throughout Ouachita Hedge-Nettle’s range. These plants are are in need of further taxonomic study.

Article and photographs by ANPS member Sid Vogelpohl

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