Inflorescences

What is an inflorescence?

An inflorescence is a cluster of flowers arranged along a stem.
The branching of the flowering stalk creates most of the inflorescence types
Inflorescences contain pedicels (stem that directly holds a flower) and peduncles (stems that support other stems and pedicels)
There are several types of inflorescences:

Above: The spike of flowers in mullein (Verbascum thapsus)

Above: The raceme of Grape hyacinth (Muscari)

Above: A panicle of Butterfly Bush (Buddleja)

A spike-like inflorescence of unisexual flowers
Catkins are usually wind-pollinated and lack petals
Typical inflorescence of willow (Salix), cottonwood (Populus), oak (Quercus), alder (Alnus), and birch (Betula)
This feature has evolved several times, in different groups of angiosperms

Above: A male catkin of Cottonwood (Populus)

A group of flowers in which the oldest flower terminates the main axis, and the inflorescence continues branching through axillary buds
Scorpioid cymes have 1-sides branching, forming a coiled inflorescence
e.g. Boraginaceae (forget-me-not family) and Hydrophyllaceae (waterleaf family)

Above: Scorpioid cyme of the Boraginaceae

All flower stalks (pedicels) originate from the same point with equal lengths, creating a flat-topped appearance
Simple umbel: inflorescence contains a peduncle and several equal-length pedicels
Compound umbel: inflorescence contains a peduncle, which gives rise to several "rays", which give rise to equal-length pedicels
e.g. Apiaceae (carrot family), Asclepidaceae (milkweed family)

Above: simple umbel of milkweed (Asclepias)

Above: Compound umbel of Queen Anne's Lace (Daucus carota)

Similar in branching to a panicle, but similar in shape to an umbel
The proximal (lower) flowers have longer pedicels
The pedicels become shorter with more distal flowers
The result is an inflorescence with a flat top appearance
e.g. Yarrow (Achillea), many species in the Maloideae, such as hawthorns and Sorbus

Above: The corymb of Yarrow (Achillea millefolium)

Inflorescence in which many flowers are attached to a dome-like receptacle, and appears to be 1 flower
e.g. Daisy family (Asteraceae or Compositae)

Bilateral flowers, with fused petals, that make the entire ray flower look like 1 petal

Radial flowers, fused at the base, that form the "eye" of a composite inflorescence

Composite species may have a combination of disk flowers and/or ray flowers

Above: Head of a composite inflorescence (Ursinia) with both disk and ray flowers

Above: Dandelion (Taraxacum officinale) is a composite with ray flowers only

Above: Pineapple weed (Matricaria discoidea) is a composite with disk flowers only

A thick, fleshy spike of unisexual flowers lacking petals (spadix), often surrounded by a vase-shaped modified leaf (spathe)
e.g. Arum family (Araceae)

Above: The spadix and spathe of wild arum (Arum maculatum)

The talipot palm (Corypha umbraculifera) has the largest inflorescence in the world
- The inflorescences of many palms (Arecaceae) are panicles
The inflorescence grows up to 25 m (80 ft) with stems up to 1.3 m (4.25 ft) in diameter
This palm grows in eastern and southern India and Sri Lanka

Above: The inflorescence of the talipot palm (Corypha umbraculifera); the largest in the world

The largest unbranched inflorescence is the titan arum, Amorphophallus titanum
- The titan arum is in the Araceae, which means that it has a spathe and spadix inflorescence
The inflorescence grows over 3m (10 ft )
It is native to western Sumatra but is commonly grown and displayed at botanical gardens

Above: the spathe and spadix inflorescence of the Titan Arum (Amorphophallus titanum)