Know Your Natives – Betony-Leaf Noseburn

Betony-Leaf Noseburn (Tragia betonicifolia) of the Spurge (Euphorbiaceae) family is a perennial monoecious forb that is well-clad in stinging hairs. The genus name honors Hieronymus Tragus (aka Hieronymus Bock, a 16th-century German botanist). The species epithet is Latin for “betony leaved” and associates the appearance of leaves of this species to the Eurasian Betony (Betonica officinalis). The species occurs in the south-central U.S. from Texas and Louisiana north to Kansas and Missouri, with disjunct occurrences in Tennessee. In Arkansas, it occurs in well-drained areas of the western West Gulf Coastal Plain but primarily throughout large sections of the Interior Highlands. Preferred habitats include dry sandy to rocky soils in prairies, woodland openings, and glades, in both acidic and basic soils.

Betony-Leaf Noseburn, with long-ropy descending and spreading branched roots and stout caudex, is inconspicuous when growing with other species of similar height. It is a lanky, multi-stemmed plant. Early stems are erect but become leaning with growth, unless supported. Depending on environment and degree of support and shading, stems, grow to 2½ feet tall and have a near-ground diameter of about 1/16 inch. They are terete in cross-section, medium green, unbranched or sparsely branched, with closely spaced, slight longitudinal ridges. Branches, mostly about mid-stem, are axillary to alternate leaves. The stems and branches may twine. The entire plant, to varying degrees, has a fine translucent pubescence with stinging hairs. Hairs on stems align with the longitudinal ridges. Winter-killed stems persist well into the next growth year(s) so that the caudex is spiky.

yPhoto 1: The branched ropy roots of this plant grew in a rock-free, fine-sandy soil. Dead stems of the previous year persist, along with stumps of earlier years. Photo July 12.
Photo 2: Spring growth is heavily pubescent. This same plant is shown in Photo 1. Photo – May 14.
Photo 3: These two stems, growing with support, developed long axillary branches. Left stem is 30 inches long with 21 inches shown. Photo – July 13.

The lanceolate to broadly lanceolate alternate leaves, to 2½ inches long and 1 inch wide (including petioles to ¾ inch), have acuminate apexes and, typically, cordate bases. Pinnate venation is recessed above and strongly expressed below. Lateral margins have prominent round-triangular serrations with tiny pin-tips––the termination of secondary veins. Straight slender petioles (1/32 inch wide) are ascending at 45⁰, but the blade midribs arch downward so that the entire leaf blade is angled downward. Upper and lower leaf surfaces are a medium green with the lower surface duller. Pubescence of upper blade surface is very short, sparse and appressed while that of the lower surface is significantly longer and dense along major veins. Leaves are well spaced at ½ to 2 inches apart. A pair of lanceolate stipules, less than ⅛ inch long, occurs at the base of leaves, but dry and wither during the growing season.

Photo 4: Leaves typically have cordate bases. Prominent pinnate venation is recessed above and strongly expressed below. Stems, along with other parts of the plant, are densely pubescent with stinging hairs. Photo – May 30.
Photo 5: Right leaf pair are from low on stem while left pair is from mid-stem. A terminal stem segment is shown above. Stipules at base of petioles have dried. Photo – July 14.

With indeterminate plant growth, flowering may continue at the ends of stems from spring into summer. Whereas branches are axillary, the inflorescence is borne on short leafless stems (floral stems) growing opposite leaf-bases. Floral stems, to about ¾ inch long, develop along with leaves at the elongating tips of stems and branches. Near the base of floral stems, a “limb,” with several linear bracts, diverges from the main stem to a pedicel (marked by a joint) that supports a pistillate flower (see Photo 7). From the base of the limb, the floral stem continues as a raceme bearing 10 to 30 staminate flowers. Staminate flowers on stubby pedicels are subtended by linear bracts. Floral stems, limbs, pedicels and bracts are a medium green with dense straight to twisty stinging pubescence.

Photo 6: Floral stems, growing opposite leaf bases, develop when leaves appear at tips of elongating stems. Several floral stems, about ¾ inch long, can be seen on which staminate flowers have dropped as fruits mature. Photo – July 14.

The ovary of a pistillate flower comprises 3 large spherical, joined carpels which have a dense covering of large, translucent, stinging hairs. Pistillate flowers, set on a calyx composed of about five elongate-triangular sepals, lack petals and have a central set of three fused stubby styles; each topped with a spreading stigma.

Photo 7: Floral stems bear a pistillate flower and a raceme of staminate flowers. Red arrow indicates pedicel of the pistillate flower. Yellow arrow indicates pedicel of a discarded staminate flower. Note bracts subtending staminate flowers and bracts on “limb” below pistillate flower. Photo – June 30.

Photo 8: Pistillate flowers have 3 fused styles, each topped with an outward-spreading stigma. Longest hairs occur on fruit. Photo – June 30.

Staminate flowers bloom sequentially from raceme base to apex and may complete flowering before the pistillate flower reaches anthesis. The less than 1/16-inch-wide greenish yellow staminate flowers have 3 sepals, no petals, and 3 paddle-shaped pale yellow filaments topped with pale yellow anthers with the shape of a vertically oriented knob. Sepals, flared and petal-like, join to form a tube attached to a very stubby pedicel. With the passing of anthesis, staminate flowers drop off, leaving short, stubby pedicels and subtending dark green lanceolate bracts. The pedicels of Betony-Leaf Noseburn are considerably shorter than the bracts, a helpful trait for identifying the species. The empty raceme persists as the fruits dry.

Photo 9: The greenish yellow staminate flowers, less than 1/16 inch wide, have 3 sepals and stamens. Once the pale yellow pollen is released, flowers quickly drop off. Photo – June 30.

With fertilization, a 3-chambered, green, 1/4-inch seed capsule develops, becoming tan as it dries and matures. Capsules kinetically dehisce, resulting in a partial separation of the two sections of each chamber and a small “blow-out” of the lower portion of each chamber. Each chamber produces a single seed. With seeds dispersed, the “damaged” chambers drop to the ground, still intact. The black spherical seeds (⅛+ inch in diameter) are hard with a thin, elongate hilum.

Photo 10: On left, floral stem grows opposite a leaf that has a pair of stipules at its base. Staminate flowers have dropped off the raceme as fruit matures. Central scar of the styles can be seen on fruit at right. Photo – August 17.
Photo 11: When dry, simultaneously, chambers kinetically dehisce with seams widening slightly as seeds are ejected through the chambers’ bases. The black spherical seeds are hard with a thin, elongate hilum. Squares = ¼ inch. Photo – July 14.

For gardening purposes, this interesting plant should probably be relegated to a naturalistic garden where it would not likely come in contact with people. A slight touch of its stinging hairs to wrists, ankles, etc. can cause irritation for 10 to 15 minutes. Another species with stinging hairs addressed by this series of articles is Wood Nettle (Laportea canadensis).

Four other species of Noseburn occur in Arkansas: Heart-Leaf Noseburn (T. cordata), Branched Noseburn (T. ramosa), Small’s Noseburn (T. smallii), and Nettle-Leaf Noseburn (T. urticifolia). Heart-Leaf Noseburn has large, heart-shaped leaves with long acuminate tips and numerous teeth per side. It grows in moist forests in several areas of the state. Branched Noseburn has linear leaves. It is found primarily in calcareous glades in the Ozark Highlands. Small’s Noseburn has rounded leaves with few, broad teeth. In Arkansas, it is found only in the sandhills of Miller County and is a state species of conservation concern. Nettle-Leaf Noseburn is the most similar to and easily confused with Betony-Leaf Noseburn. The primary character that distinguishes it is that the staminate flower pedicels of Nettle-Leaf Noseburn are about equal to or slightly exceed the bracts. Nettle-Leaf Noseburn is found primarily in better drained areas of the West Gulf Coastal Plain and southern Ouachita Mountains, in primarily acidic soils.

Article and photographs by ANPS member Sid Vogelpohl

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