thickhead

Crassocephalum crepidioides
Herb
Alternate
Simple
Red
Pink
Purple
Orange
Green

A short-lived herbaceous plant with upright stems growing up to 1.5 m tall. Its alternately arranged leaves (4-20 cm long) have irregularly toothed margins. The lower leaves are sometimes deeply lobed, while the smaller upper leaves tend not to be lobed.

  • its drooping flower-heads are borne in loose clusters at the top of the plant.
  • these orange, reddish, pinkish or purplish flower-heads (about 10 mm long) are cylindrical in shape and have no 'petals'. Its tiny 'seeds' (about 2 mm long) are topped with a tuft of silky hairs 8-12 mm long.
  • Common names 
    Also known as: fireweed, hawksbeard velvetplant, redflower ragleaf, thick head, thickhead,
    Family 
    Asteraceae
    Deciduous 
    No
    Flowering time 
    Year round
    Native/Exotic 
    Exotic
    Origin 
    Native to sub-Saharan Africa.
    Notifiable 
    No
    Council declaration 
    SIL – Special Investigation List
    Known distribution 

    Widely naturalised and common in the coastal districts of south-eastern Queensland (i.e. in the Moreton and Wide Bay districts). Also naturalised in the coastal and sub-coastal districts of northern and central New South Wales, on Norfolk Island, and on Christmas Island.

    Habitat 

    Primarily a weed of crops, fallows, orchards, forestry plantations, parks, gardens, waste areas, disturbed sites and roadsides. But also a relatively common weed of riparian vegetation, forest gaps and margins, coastal environs and open woodlands.

    Habit 

    A short-lived (i.e. annual) herbaceous plant with upright (i.e. erect) stems growing up to 1.5 m tall.

    Impact and control methods 
    Stem and leaves 

    The stems are hairless (i.e. glabrous) or sparsely hairy (i.e. pubescent). The leaves are alternately arranged along the stems and are borne on stalks (i.e. petioles) 0.5-4 cm long. These leaves (4-20 cm long and 1-10 cm wide) are more or less egg-shaped in outline (i.e. ovate) or oval (i.e. elliptic) in shape with irregularly toothed (i.e. serrate) margins and a pointed tip (i.e. acute apex). The lower leaves are sometimes deeply lobed, with the upper lobe larger than the others (i.e. lyrate-pinnatifid). The smaller upper leaves tend not to be lobed, but if they are lobed then they only have a pair of small lobes at the base of the leaf blade. Leaves are hairless (i.e. glabrous) or very sparsely hairy (i.e. puberulous).

    Flowers and fruits 

    The flower-heads (i.e. capitula) are borne in loose clusters at the top of the plant (i.e. terminal corymbose cymes). These orange, reddish, pinkish or purplish flower-heads (about 10 mm long and 4 mm wide) are cylindrical in shape and have no 'petals' (i.e. ray florets). They droop at first, but eventually become upright as the wind-blown seeds mature. Each flower-head has numerous tiny flowers (i.e. tubular or disc florets) that are surrounded by two rows (i.e. involucre) of green bracts. The outer row of bracts is very small (1-2 mm long), while the inner row is much longer (8-12 mm long). Flowering occurs throughout the year, but mainly during summer. The narrow 'seeds' (i.e. achenes or cypselae) are dark brown or reddish-brown in colour and ribbed lengthwise (i.e. longitudinally). These 'seeds' (about 2 mm long) are topped with a tuft (i.e. pappus) of silky hairs 8-12 mm long. The white hairs are often tinged with reddish or mauve and readily fall off.

    Reproduction and dispersal 

    This species reproduces only by seed, which are easily blown and dispersed by the wind. Seeds may also be spread by machinery, water, vehicles, animals, and in clothing and contaminated agricultural produce.

    Similar species 

    Emilia (Emilia sonchifolia var. javanica) has many attributes that are similar to thickhead (Crassocephalum crepidioides). It has pinkish coloured cylindrical flower-heads without any 'petals' (i.e. ray florets), and produces similar wind-blown seeds. However, the flower-heads of emilia (Emilia sonchifolia var. javanica ) do not droop and are usually bright pink in colour, while its leaves are often somewhat hairy.