Stems & Roots: Stems erect, 20-90cm (8-36in.) high, branching in
the upper part, harshly hairy near the base but weakly hairy or smooth upwards,
greenish or sometimes purplish.
Leaves: Seedling with broad kidney-shaped cotyledons; stem leaves alternate
(1 per node), somewhat hairy; lowermost leaves on young plants long-stalked
and either without lobes or with shallow to deep lobes near the base of the
blade; upper leaves stalkless and coarsely toothed but usually not lobed.
Flowers & Fruit: Flowers in small clusters which lengthen
as the seedpods develop, bright lemon yellow, about 1.5cm (3/5in.) across
with 4 small sepals, 4 larger petals arranged in the form of a cross (Family
name "Cruciferae" means crucifix or cross), 4 long and 2 short stamens (total
6) and 1 slender pistil; flower stalks thin and short (3-5mm, 1/8-1/5in.
long), becoming thicker but not longer as the seedpods develop, sometimes
nearly as thick as the pod itself; seedpods (siliques) 3-5cm (1¼-2in.)
long, sometimes bristly hairy but usually without hair, often with lengthwise
ribs, erect and pressed to the stem or spreading out; each pod has a flattened
terminal beak with 1 or rarely 2 seeds in its base and a main section containing
several seeds which are released when the 2 sides or valves split apart from
the bottom end and fall away entirely; seeds spherical, 1.5mm (1/16in.) in
diameter, black or purplish. Flowering may begin as early as late May and
continue throughout the summer.
Habitat: Wild mustard occurs throughout Ontario, being most frequent
in cultivated fields and gardens, but occasionally appearing in fence lines,
along roadsides and in waste areas.
Similar Species: It is distinguished from similar mustards by its somewhat
kidney-shaped cotyledons being broad with a deep, wide, rounded notch at
the end, the hairy stem with lower leaves stalked and either lobed or unlobed
but upper ones stalkless and merely toothed, its large flowers and its seedpod
with a short thick stalk and a flat beak that is about 1/3 the total length
of the pod and usually contains an additional seed or two; and from Yellow
rocket by being annual with hairy stems, its lemon-yellow flowers usually
not appearing before late May and its seedpods on short, thick stalks and
having a prominent, flat beak containing 1 or 2 seeds.
