Ontario Weeds: Hoary alyssum

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Excerpt from Publication 505, Ontario Weeds, Order this publication

Table of Contents

  1. Name
  2. Other Names
  3. Family
  4. General Description
  5. Stems and Roots
  6. Leaves
  7. Flowers and Fruit
  8. Habitat
  9. Similar Species
  10. Related Links

Name: Hoary alyssum, Berteroa incana (L.) DC,

Other Names: berteroa blanche, alysse

Family: Mustard Family (Cruciferae

General Description: Annual or short-lived perennial, reproducing only by seed.

Photos and Pictures

Hoary alyssum.

Hoary alyssum. A. Base of plant. B. Top of flowering and fruiting stem.

Hoary alyssum. A. Base of plant. B. Top of flowering and fruiting stem.

Stems & Roots: Stems - erect, 20-70cm (8-28in.) high, usually branched above and frequently purplish; green or each plant with 1 to many stems per plant;

Leaves: First leaves in a basal rosette, long-stalked, broadest near the tip; middle leaves similar but smaller; upper leaves stalkless, either elliptic or broader near the base, tapering to a long narrow point; all leaves alternate (1 per node), entire (without teeth) and not clasping the stem; stems, leaves, sepals and seedpods covered with very short star-shaped hairs giving the whole plant a gray hoary appearance;

Flowers & Fruit: Flowers like Wild mustard but smaller (3mm, 1/8in. across) with deeply lobed, white petals, clustered near the tips of the stems and branches; seedpods on erect stalks and held close to the stem; pods elliptical or oval, 5-8mm (1/5-1/3in.) long by 3-4mm (1/8-1/6in.) wide, slightly flattened; septum (membranous partition) as wide as the greatest width of the pod and usually remaining on the stalk after the sides of the pod have fallen off when mature, each pod containing 4 to 12 reddish-brown to brownish lens-shaped seeds 1-1.5mm (1/25-1/16in.) long with a faint suggestion of a wing around the edge. Flowers from late May to autumn, maturing and shedding seeds throughout the summer.

Habitat: Hoary alyssum occurs throughout Ontario but is more common in the southern part, particularly on sandy soils. It is found in hay and pasture fields, meadows, roadsides, waste areas and occasionally in gardens or poorly kept lawns.

Similar Species: It is distinguished from other mustards with rounded seedpods by its stalkless, non-clasping stem leaves with smooth (entire) margins, the dense star-shaped hairs that give the whole plant a hoary appearance, and the broad septum (membranous partition) in the oval, hoary seedpods which are held erect and very close to the stem.

Related Links

... on general Weed topics
... on weed identification, order OMAFRA Publication 505: Ontario Weeds
... on weed control, order OMAFRA Publication 75: Guide To Weed Control

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