The species plant is an annual herb native to Mexico.
The small sparsely branched plants have opposite, directly attached leaves.
The solitary flower heads, a few cms across are on a long peduncle.
They have around 8 to 12 red edge ray florets and many dense disc florets.
The garden plants are hybrids sometimes known as Zinnia violacea.
These Common or Garden zinnias vary from species plant in height and branching but mostly in the flower heads.
Heads are larger and come in a huge range of colours.
There are hundreds of cultivars and the description below is of these.
There are small areas of naturalised plants in Queensland.
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There are low mounding plants around 15 cm high to variably branched plants over 1 m.
The sometimes ribbed stems are green, yellow or purplish.
There may be no hairs up to dense simple or branched ones.
The opposite leaves, up to 12 or 13 cm long are directly attached to the stems.
Up to 7 cm wide the blades can be linear, ovate, oblong or lance-shaped.
The tips are pointed and the base may be flat or heart-shaped and clasping the stem.
The surfaces may have glands or hairs and the edges smooth or with tiny hairs (cilia).
Inflorescences are a solitary terminal flower head or capitulum.
The ribbed peduncles, up to 15 cm long may have dense hairs.
Heads, with both ray and disc florets can be up to 15 cm across.
The receptacle can be slightly convex or up to around 2 cm high.
Scales or paleae (chaff) on the receptacle are shorter than the flowers they surround.
The narrow palea, with a deeply fringed tip change from green to reddish to purple.
The involucre at the base of the head has 3 to 5 series of free, overlapping bracts or phyllaries.
The outer ones are a few mms long with the inner ones up to 1 cm.
They have a rounded tip that is slightly fringed.
The obovate hairless green bracts usually have dark edge.
Ray florets can be in a single row up to almost replacing the disc florets.
This gives single, semi-double and double forms up to pompoms.
The 5 petals are joined to form a ligule up to 3 or 3.5 cm long.
The base of the obovate or spoon-shaped ligule has hairs on the outer surface.
The ligule may be wide or narrow and straight or twisted.
They come in white and shades of all colours except blue and some are bi-coloured.
Rays are fertile females with a single ovule in the inferior ovary.
The bisexual yellow disk florets have a corolla tube around 8 mm long and 5 lobes 1 to 2 mm long.
The filaments of the 5 stamens are free and the fused black anthers form a tube around the style.
The anthers have a sterile apical appendage.
The style has 2 flat stigma lobes with hairs and the ovary is similar to that of the ray florets.
Both ray and disk florets produce a single flattened fruit.
Commonly called an achene they are a cypsela as they come from an inferior ovary and have one seed.
Fruit from the ray florets are around 8 mm long and 5 mm across.
They are 3-angled with one angle being more prominent than the others.
They have no awn (bristle) but usually have tiny stiff hairs.
Disc cypselae are more flattened with narrow lateral wings.
They are smaller being mostly around 6 mm long.
There may be no pappus, awn or hairs but some have a short pappus, a single awn or edge hairs.
J.F.
