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Aquatic and Wetland Vascular Plants of the Northern Great Plains

31. Onagraceae, the Evening Primrose Family

2. Epilobium L. -- Willow herb

1. Epilobium ciliatum Raf.


Simple and erect to branched and spreading perennial, flowering the first year, producing overwintering above-ground leafy rosettes or subterranean fleshy turions at the base in autumn, (0.3)1.5-8(12) dm tall; stems glabrous below, sparingly to densely pubescent above, with short eglandular hairs intermixed with long glandular hairs, especially pubescent on the decurrent leaf bases and in the inflorescence. Leaves opposite below or for much of the length of the stem, usually alternate above, at least in the inflorescence, sessile or with short winged petioles to 6 mm long, the blades lanceolate to ovate-lanceolate, 2.5-9(12) cm long, 0.8-3(4.5) cm wide, acute or acuminate to a rather blunt tip, irregularly and shallowly serrate, mostly with 15-30 teeth on each margin, rounded at the base. Floral tube 0.5-2.5 mm long; sepals ovate, acute, 1.5-5 mm long, not projecting or divergent in bud, the tips forming an obtuse to rounded or slightly pointed bud apex; petals whitish to pink, 1.5-10(12) mm long, strongly notched; pedicels mostly 3-10 mm long. Capsules linear, 3-7(10) cm long, pubescent; seeds mostly 0.8-1.6 mm long, longitudinally striate with hyaline crests or ridges, usually not papillate, the coma white or nearly so, attached to a short, broad, flattened beak at the tip of the seed. Jul--Sep. Shores, stream banks, marshes, wet meadows, springs, seepage areas, ditches and other wet places; common; (Newf. and Labr. to AK, s to NC, TN, OH, IA, TX and AZ; also Mex. and C.Amer., Japan and Korea).

Two subspecies occur in the northern Great Plains and they are distinguished as follows:

1a. subsp. ciliatum. Plants usually producing above-ground leafy rosettes in fall; cauline leaves narrowly lanceolate to narrowly ovate; inflorescence non-leafy, branched; petals white to pink, 1.5-5(8) mm long; seeds (0.6)0.8-1.2(1.5) mm long. Occasional in NE and perhaps s SD.

1b. subsp. glandulosum (Lehm.) Hoch & Raven. Plants usually producing reddish, subterranean turions with fleshy, imbricate leaves in the fall; cauline leaves broader; inflorescence mostly leafy, unbranched; petals pink to rose-purple, rarely white, 3.5-10(12) mm long; seeds 1.1-1.6(1.9) mm long. Common throughout. E. glandulosum Lehm. var. adenocaulon (Hausskn.) Fern., E. adenocaulon Hausskn.

Also reported for the Black Hills are three species similar to though apparently much less common than E. ciliatum: E. halleanum Hausskn., E. hornemannii Reichenb. and E. saximontanum. They may be distinguished from E. ciliatum and each other by the following key:

1	Plants clumped or cespitose, forming short, leafy, above-ground
	shoots at the base; stem decumbent to ascending at the base;
	leaves petiolate .................. E. hornemannii

1	Plants not clumped or only loosely clumped, forming sessile,
	leafy rosettes or fleshy turions; stem erect at the base; leaves
	sessile to occasionally petiolate.

	2	Plants 0.3-19 dm tall, forming leafy rosettes or large,
		subterranean turions; seeds 0.8-1.6(1.9) mm long,
		longitudinally striate with hyaline crests or ridges but
		lacking distinct papillae ......... E. ciliatum

	2	Plants 0.2-6 dm tall, lacking rosettes, forming only
		compact subterranean turions; seeds 1.1-1.6(1.8) mm long,
		distinctly papillate, the papillae often in longitudinal
		rows.

		3	Leaves sessile, clasping, mostly narrowly ovate,
			denticulate; turions fleshy, elongate; capsules
			subsessile, appressed; seed collar conspicuous
			below the coma ........... E. saximontanum

		3	Leaves petiolate or subsessile, not clasping,
			lanceolate or narrower, subentire or denticulate;
			turions compact, round; capsules on pedicels
			0.8-3.8 cm long; seed collar inconspicuous ......
			....... E. halleanum
GIF- Species Photo/Drawing
GIF- Distribution Map

Map key

Epilobium ciliatum.  

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