Zea are in Family Poaceae > Subfamily Panicoideae.
Maize (corn) was originally from, and domesticated in, Mexico.
Plants of the World Online (Kew) accepts 7 species, others 4 or 5 with subspecies.
Some say just one variable species that is probably an ancient hybrid.
Australia has 2 naturalised species Zea mays and Zea mexicana.
The mostly annual grasses have one erect stem or culm up to around 5 m.
Wide lance-shaped or linear leaves are alternate and in 2 ranks (distichous).
The top of the leaf sheath on the stem has a ligule (appendage).
Plants are monoecious with separate male and female inflorescences on the same plant.
(Early in their development all inflorescences have bisexual flowers).
The basic inflorescence unit is a raceme with flowers along a midrib and the lower ones opening first.
Female inflorescences have 1 raceme.
Male inflorescences have numerous racemes that can be attached to the tip of the stem or in a branched cluster (panicle).
The former look like tassels and the name is applied to all male inflorescences.
Each raceme has 1 or more spikelets attached to the midrib.
At the base of each flattened spikelet is a pair of wide bracts called glumes.
A spikelet consists of 2 florets.
A floret has 1 flower and 2 bracts – the outer lemma and the smaller inner palea.
In male inflorescences the flower is reduced to 3 stamens.
Female inflorescences develop from the axillary leaf buds which are short lateral branches.
The leaves become the husks and the end of the stem becomes the woody cob.
The husks (spathe, bract) are modified leaves that tightly surround the cob.
Most of a husk is the long wide leaf sheath that has open edges.
The small deciduous leaf blade at the top is linear to lance-shaped.
At the blade to sheath junction is a membranous ligule.
The tip of the short axillary bud stem becomes the tough midrib of the raceme.
Known as the cob it can be up to 30 cm long.
Along the cob are a few up to 30 rows of paired spikelets with 2 glumes at their base.
Spikelets have 2 florets each with 1 flower surrounded by a lemma and palea.
One flower is sterile, the other fertile.
Fertile flowers are reduced to an inferior ovary with 1 ovule.
The long style with 2 linear stigmas grows to the top of the cob and extends past the husks.
All the drooping tubular styles form the silk.
One pollen grain falling on a silk germinates and a pollen tube grows down the silk (hollow style) to the ovary where it fertilises the ovule.
Each fertilised ovary can develop into a kernel with yellow flesh.
Each fruit is a caryopsis with the kernel coat fused to the ovary wall.
Mature kernels are commonly yellow or white but there are over 50 different types with various patterns and colours.
With modern plants the fruit no longer fall off the cob naturally so plants cannot reproduce on their own.
J.F.
