DICOTYLEDONS
BRASSICACEAE - Cabbage Family
Formerly known as the
Cruciferae, because it has four petals held open in the shape of a
cross, this family includes many important vegetables and
agricultural crops. There are over 3000 species throughout the world,
but the largest number are from temperate regions of the Northern
Hemisphere. In Western Australia there are 54 native species and
about 40 naturalised. Several have bright yellow flowers and can be
difficult to distinguish from each other before fruits have formed.
As a result, some species may be overlooked when in flower, by
assuming that they are more familiar species. Identification
therefore often relies on the presence of mature fruits. The fruits
may have a "beak" at the end and are often divided internally by a
longitudinal septum. For identification purposes, the family is
usually divided into those species with fruits more than three times
as long as broad (excluding the 'beak'), in which case the fruit is
termed a siliqua, and those in which they are less than three times
as long as broad, in which case the fruit is referred to as a
silicula.
Alyssum
linifolium
(flax-leaf alyssum) is an annual herb, up to about 30cm. The leaves
are narrow, grey, and densely covered in short hairs. The fruit pod
is a silicula up to 6mm long, flattened parallel to the septum,
containing four to six seeds on each side. It flowers in spring and
the white petals are 2-3mm long. It is a scattered weed of woodlands
in the Goldfields and is native to southern Europe, western Asia and
possibly also to Australia.
Eight species of the genus
Brassica
have been recorded as weeds in Western Australia. Although pictures
of only one is shown here, it is important to distinguish between
them; some species may be under-recorded because of incorrect
identification.
B. barrelieri
subsp. oxyrrhina (was B.
oxyrrhina)
(smooth-stem turnip) is an annual to 50cm. Its leaves are pinnately
divided with the sharp lobes pointing towards the leaf base and stiff
hairs on the undersurface of the midrib. The stem of the
inflorescence is only slightly hairy at the base or not at all. The
petals are 6-8mm, white or pale yellow with distinct purple veins.
The fruit is a siliqua, 2.5 to 6cm long with a beak (containing one
or two seeds) 1-3mm long. It flowers in spring and is recorded
occasionally from the wheatbelt, disturbed coastal sites and road
verges in Perth. Probably more common than currently recorded. Native
to the Iberian Peninsula.
B.
fruticulosa
(twiggy turnip) is an annual or short-lived perennial, up to 50cm
tall. It is one of the least leafy of the introduced
Brassica
species. The petals are pale yellow, about 10mm long. The flowers are
produced in spring and summer. The narrow siliquas are 2-4cm long and
constricted around the seeds, giving them a knobbly appearance. It is
a weed of urban waste ground and railway lines. It has been recorded
from a few locations in Perth and probably has the potential to
spread in urban and horticultural areas. Native to the Mediterranean.
Possibly introduced as a vegetable.
B.
juncea (Indian
mustard) is an annual, up to 1m tall. The leaves are blue-green. The
petals are 7-9mm long, pale yellow and the fruit 2-6cm long, with a
beak more than 4mm. It can be distinguished from B. rapa,
B.
oleracea and
B.
napus by its
stalked upper stem leaves. This species is occasionally grown as a
crop in Western Australia, probably the source of its introduction.
However, although widespread in agricultural areas, it is not common.
Native of Europe and Asia. Flowers in spring.
B. napus (oilseed rape, rapeseed, canola) is now becoming a widespread
crop, and this annual species is found commonly along roadsides in
the south-west of the State, where it may have spilt from trucks.
However, these populations often seem to persist under these
disturbed conditions. Leaves are blue-green (unlike
B.
rapa), those at
the base may be bristly. The petals are 11-14mm, bright yellow. The
fruits are 4.5 to 10cm long. Its stems may reach 1.5m, but along road
verges it is usually much shorter. Flowers in spring. May have
originated as a hybrid of B.
oleracea and
B. rapa.
B.
oleracea
includes cabbage, broccoli and cauliflower among its various
cultivated forms. In the weedy form, the leaves are
blue-green (in contrast to B.
rapa) and completely hairless. It is an annual, to 1m.
The petals are 10-20mm long, usually longer than
B. napus.
It flowers in spring. Its fruits can be among the longest of
the Brassica species in Western Australia, up to 10cm. It is an
occasional weed in the south-west of the State. Native of
Europe. B.
rapa
(turnip) is an annual to 1m, and is the weedy form of the
vegetable turnip. Along with B. napus
and B.
oleracea,
the upper leaves clasp around the stem. Unlike those
species, its leaves are a bright green and its petals are
the brightest yellow and the lower leaves may be bristly.
The fruit is a siliqua, 4-6.5cm long. It has probably
escaped from cultivation, but where it occurs as a weed, its
root does not swell as in the vegetable form. It is
infrequently reported as an agricultural weed; in some
areas, such as Albany, it can be the dominant weed in market
gardens.
B.
nigra (black
mustard) is an annual, to 1m. The flowers are bright yellow, with
petals 7-9mm long. The fruit pods are 1-2cm long, the beak less than
4mm. The lower leaves are bristly. The only naturalised species of
Brassica
with its fruits, that are distinctly four-sided, held closely along
the main stem on maturity. Occasionally recorded as a weed of
cropping in the south-west of Western Australia. Formerly grown as a
crop. A native of Europe.
B.
tournefortii
(wild turnip) is an annual to 60cm. The leaves are pinnate,
with sharp lobes pointing backwards towards the leaf base
and densely covered with bristles, particularly on the
underside. The inflorescence is densely hairy, although
hairs become sparser towards the top. the petals are pale
yellow or cream to white, 5-8mm long. The fruit is a
siliqua, 3-7cm long with a beak 1-2cm long. It is a common
weed of wasteland, roadsides, grazed woodlands, shrublands
and islands; a widespread weed of horticulture and of crops
in the agricultural areas. Found from Carnarvon to
Eucla.
Brassica
tournefortii
, RR
Brassicaceae
continued
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