Know Your Natives – Fly poison

Fly poison (Amianthium muscitoxicum*) of the Bunchflower (Melanthiaceae) family, the only species in the genus, bears white flowers that change to green. The genus name originates from Greek words for “pure” and “flower”. The specific epithet is from Latin words for “fly” and “poison”. In the U.S., fly poison occurs from Oklahoma and Missouri across the Southeast and extending north into New York. In Arkansas, it occurs primarily in scattered Interior Highlands counties in roughly the northwestern half of the state. The name “fly poison” relates to early Americans’ use of the plant’s bulbs (crushed with a sweetener) to kill flies. Other common names include crow poison (used by Native Americans to poison crows) and stagger grass (causes grazing cattle to stagger). The plant is generally found in dry to moist open woodlands and prairies. Along with the bulb, other parts of the plant are also poisonous, although to a lesser degree.

Seedlings (monocots) have contractile roots which pull the bulb’s base several inches into the earth so that tops of bulbs are just below the surface. Numerous white fleshy roots, newly grown each year, splay in all directions from the reduced stem at the base of the bulb (basal plate). Mature bulbs, slender with a broader lower section, are to 2 inches long and to 1 to 1¼ inches wide. Tight clumps of bulbs may form as clonal bulbs develop off basal plates. Girth of bulbs increases as new concentric leaf bases (fleshy scales), terminated by a leaf, grow from the interior-center of the basal plate. Old leaf bases thin and dry on the exterior to form a papery tunic. Basal plates typically have one vegetative growth point, but a second point may develop.

In late winter, a bulb produces eight to a dozen new leaves as an upright rosette, surrounded by limp dead leaves and maybe a dead stem from the previous growing season. Leaves may reach a length of 2 feet at maturity. Leaves, a bright medium green, are broadly arched with the tips touching the ground. Leaf width, ½ to ¾ inches, is fairly uniform except for a widened base and a short-tapered cupped tip. In cross section, leaves are v-shaped with a channeled upper midrib and a sharply keeled lower midrib. Leaf margins are entire. Closely spaced veins parallel the straight, entire (undivided) margins. Leaves begin to fade in early August as fruit develop.

Fly Poison - Amianthium muscitoxicumPhoto 1: Leaf rosettes appear in late winter. Tips of leaves are cupped. Photo March 18.

Fly Poison - Amianthium muscitoxicumPhoto 2: This clonal group produced several rosettes of arching leaves. Upper mid-veins are channeled.

In early May, flowering stems, same color as leaves, rise above leaves from the center of leaf rosettes. A few bulbs of a colony each produce single, unbranched, erect stems. Glabrous stems grow to 3 feet tall and about ¼ inch wide, with three smoothly rounded sides. Stems have three or so widely spaced and clasping leaves on the lower half that transition into a half dozen or more closely spaced bracts on the upper half. Cauline leaves are helically (spirally) alternate. Lowermost cauline leaves may be 16 inches long and ¾ inch wide, while uppermost cauline bracts may be ⅛ inch long and 1/16 inch wide. These small cauline bracts extend to the base of a terminal raceme. The stem within the raceme (rachis), pedicels and flowers are white. The slender, straight pedicels are ½ to ¼ inch long, radiating outward slightly above horizontal. Racemes, changing from pyramidal to cylindric and bearing up to 100 flowers, are up to 3+ inches long and up to 1¾ inches wide. Flowers bloom from bottom to top of the raceme in sequential tiers. Racemes narrow slightly from base to apex due to higher flowers being slightly smaller and pedicels being shorter.

Fly Poison - Amianthium muscitoxicumPhoto 3: Flower buds are covered by cupped bracts that quickly shrink away from buds and become brown. Long, clasping cauline leaves can be seen on the taller stem. Photo May 6.

Fly Poison - Amianthium muscitoxicumPhoto 4: Racemes are pyramidal at first, but become cylindrical as upper flowers mature. Narrow stems hold flowers well above the leaves. Photo May 20.

Flower buds are subtended and covered by cupped floral bracts which quickly shrink and become brown as flowers approach anthesis. Flowers are about ⅜ inch wide. A flower has 6 cupped tepals (3 sepals and 3 petals), 6 stamens and a short pistil with three flared and pointed styles above a prominent, free-standing, 3-chambered ovary. Each chamber is round with a sharp tip, with the chambers joined along a central axis. Sepals and petals, are reflexed and have a similar appearance; however, sepals are slightly shorter and broader. Tepals, with little lateral overlap, have rounded apexes and broad bases. Stamens are widely flaring and spiky, with knobby pale yellow anthers. Viewed from the front, anthers are centered over the cupped tepals. The shrunken brown floral bracts still persist as fruits mature. The entire raceme, except for discarded anthers and floral bracts, becomes green as the blooming sequence moves upward. The entire now-green raceme persists, including tepals and spiky filaments and stigmas, until fruit reach maturity; however, racemes become brown as fruit matures in August.

Fly Poison - Amianthium muscitoxicumPhoto 5: The white stem, pedicels and flowers change to green immediately after flowers pass anthesis. Brown remnants of subtending cupped floral bracts are persistent. Photo May 20.

Flowers have 1-2 ovules in each chamber of their 3-chambered ovaries. With fertilization, the ovaries swell to produce a deeply 3-lobed, horned capsule, ⅜ inch long and wide. Typically only a small proportion of flowers produce seeds, and all the ovules of a flower seldom mature to seeds. Mature seeds have a thin, fleshy, shiny orange outer seed coat. An enlarged mature seed causes a split of its chamber from the tip to the inside-center. The seeds, measuring about 3/16 inch long, are rounded-oblong with a narrowed apex. The seed within the outer coat is stubby and rounded, white and smooth.

Fly Poison - Amianthium muscitoxicumPhoto 6: After flowers bloom in May, the green raceme persists into August when fruits mature. Inset shows a sterile flower (bottom), a flower with seeds removed from fruit (center) and a flower with seeds retained within fruit (upper).

In a partially shady, moist garden or natural area, fly poison would provide interest from late winter into late summer. It has attractive basal leaves and a prominent long-lived white to green raceme that later shows its colorful fruit. It is not aggressive and is avoided by deer. Care must be taken so that its parts, including the onion-like bulb, are not consumed by humans or animals.

Fly poison, prior to its fruiting stage, may be confused with death camas (Toxicoscordion nuttallii).

  • The specific epithet may be spelled “muscaetoxicum”. Amianthium muscitoxicum was previously classified as Zigadenus muscitoxicus and Chrosperma muscitoxicum. Previously assigned to the Lily (Liliaceae) family.

Article and photographs by ANPS member Sid Vogelpohl

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