white rattlesnake root

not listed

N5? - Secure

SNR - Unranked

not listed

FACU - Facultative upland

FACU - Facultative upland

FACU - Facultative upland

White rattlesnake root is a 16″ to 67″ tall, erect, perennial forb that rises on usually a single stem from a taproot.

The stems are stout, erect, and sometimes branched near the top. They are light green and often mottled with purple, sometimes almost completely purple. They are hairless toward the base and inconspicuously, slightly hairy toward the tip with short, soft, curled hairs. They are often somewhat covered with a whitish, waxy bloom (glaucous).

Basal and lower stem leaves leaves are highly variable in shape. Each basal leaf is on leaf stalk (petiole) up to 7″ long. The petiole is hairy and often purple. It is not winged. The leaf blade is usually triangular-shaped, 1½″ to 11¾″ long, and 1¼″ to 7″ wide. It is sometimes arrow-shaped, with a pair of outward-turned basal lobes. It is sometimes deeply cut into three lobes, sometimes divided into three leaflets. The upper surface is hairless. The lower surface is sparsely covered with short, curled hairs, and is often somewhat glaucous. The margin has a few outward-pointed teeth. Basal leaves are present at flowering time.

Stem leaves are alternate. Lower stem leaves are on narrowly-winged petioles up to 7″ long. The petiole is shorter than or equal in length to the leaf blade. There is no large, leaf-like appendage (stipule) at the base of the petiole. The leaf blade is 1½″ to 11¾″ long, 1¼″ to 7″ wide, and highly variable in shape. It may be triangular, arrow-shaped, divided into 3 or 5 lobes, or egg-shaped. Leaves become progressively smaller, less divided, and on shorter petioles as they ascend the stem. The uppermost leaves may be stalkless, undivided, and untoothed. The upper surface is hairless. The lower surface is sparsely covered with short, curled hairs, and is often somewhat glaucous. When torn, the leaves exude a milky latex.

The inflorescence is a branched array (panicle) at the end of the stem and branches. The panicle has 2 to 4 long branches, each with a drooping cluster of 3 to 8 flower heads. The flower heads are clustered at the branch tip.

Each flower head is about ¾″ long and ½″ wide. At the base of the flower head is an involucre composed of an inner and an outer series of leaf-like appendages (bracts). The involucre is cylinder-shaped to bell-shaped, ½″ to ⅝″ long, and ⅛″ to 3 ⁄16″ wide. There are 6 to 9, usually 8, inner bracts. The inner bracts are purplish or maroon, narrowly oblong lance-shaped, ¼″ to ⅜″ long, and hairless. They are somewhat curved inward at the tip. The outer surface is whitish in appearance due to a dense covering of minute, nipple-like projections (papillae). Individual papillae can be distinguished with a 10-power hand lens. The papillae are white and appear to be covered with a waxy coating. The outer series of involucral bracts is much shorter than the inner series. There are 5 to 7 outer bracts. They are green, sometimes tinged with purple or maroon, triangular-shaped, and hairless.

There are 7 to 13, usually no more than 9, ray florets and no disk florets. The ray florets are white, sometimes tinged with pink, lavender or red near the base, and ⅜″ to ⅝″ long.

The fruit is a brown or tan, ⅛″ to ¼″ long achene (cypsela) with a tuft of feather-like hairs (pappus) attached to one end. The pappus is usually reddish-brown.

16″ to 67″

White to pale pink or lavender

Purple rattlesnake root (Nabalus racemosus) involucre bracts are hairy.

White-flowered leaf-cup (Polymnia canadensis) leaves are similar, but the petioles are not winged. The larger leaves have a large, rounded stipule at the base of the petiole that surrounds the stem. The lowest pair of lobes on pinnately-divided leaves is much reduced and is separated from the adjacent pair of lobes by a short section of winged leaf stalk.

Dry. Woods, deciduous forests. Partial sun or light shade.

August to September

Sources

2, 3, 4, 5, 7, 28, 29, 30.

Native

Common

This species was formerly classified as Prenanthes alba. In 2010, based on their close relationship with lettuce (Lactuca sativa), 24 species in the genus Prenanthes were moved to the genus Nabalus.

Plant

Inflorescence

Flowers

Buds

Basal Leaves

Lower Stem Leaves

Upper Stem Leaves

Stem