Based on branching pattern and other characters

Beyond position, inflorescences are classified by their branching pattern, the number and arrangement of their flowers, and any specialised accessory structures, into four major groups.

I. Racemose (indeterminate) inflorescence - the central axis (peduncle) keeps growing indefinitely from its terminal bud while producing lateral flowers, so the oldest flowers sit at the base and the youngest buds are near the growing apex; flower opening proceeds base-to-apex (acropetal succession), described as centripetal. Racemose types are grouped by what happens to the main axis. Where the main axis is elongated: a simple raceme bears pedicellate (stalked) flowers in acropetal succession on an unbranched axis (Crotalaria retusa, mustard, radish); a spike is similar but with sessile (stalkless) flowers (Achyranthes, Stachytarpheta); a spikelet is a small, branched spike whose branches are themselves spikelets, each sessile flower protected by a bract (lemma) and bracteole (palea), with the calyx/corolla reduced to tiny scale-like lodicules and only a stamen and pistil remaining (paddy, wheat, barley, sorghum); a catkin is a pendulous, drooping spike of small unisexual or bisexual flowers, also called an ament (Acalypha hispida, Prosopis juliflora, Piper nigrum); a spadix has a fleshy, thickened axis bearing many unisexual sessile flowers in acropetal succession (typically female flowers near the base and male flowers toward the apex), the whole cluster wrapped in a large, often brightly coloured bract called a spathe (Amorphophallus, Colocasia, Phoenix, Cocos); and a panicle is a branched raceme, also called a compound raceme or raceme of racemes (Mangifera, neem, Delonix regia). Where the main axis is shortened: a corymb has flowers of unequal pedicel length - shorter pedicels near the top, longer ones at the bottom - so all flowers reach roughly the same level, giving a flat or convex-topped cluster (Caesalpinia; a branched corymb is a compound corymb, as in cauliflower); and an umbel has an indeterminate axis whose pedicellate flowers all arise from one common point at the tip of the peduncle (Allium cepa, Centella asiatica, Memecylon umbellatum), with a branched umbel called a compound umbel, each of its smaller units an umbellule (Daucus carota, Coriandrum sativum). Where the main axis is flattened (convex, concave or globose): a head (capitulum) is a cluster of sessile or sub-sessile flowers on a flattened receptacle, often subtended by a ring of bracts called an involucre (a smaller ring below a sub-unit is an involucel) - characteristic of Asteraceae and some Rubiaceae (Neolamarkia cadamba, Mitragyna parvifolia) and also seen in Fabaceae-Mimosoideae (Acacia nilotica, Albizia lebbeck, Mimosa pudica). A head's central disc bears two kinds of florets - tubular disc florets and strap-shaped (ligulate) ray florets - and a head with only one kind of floret is homogamous (disc florets alone, e.g. Vernonia, Ageratum; or ray florets alone, e.g. Launaea, Sonchus), while one bearing both kinds is heterogamous, with bisexual tubular disc florets at the centre and unisexual, pistillate ligulate ray florets at the margin (Helianthus, Tridax).

II. Cymose (determinate) inflorescence - the central axis stops growing once it ends in a terminal flower, and any further growth comes only from axillary (lateral) buds, so the oldest flower sits at the apex/centre and younger flowers develop toward the base (basipetal succession), opening centrifugally. A simple cyme (solitary) is the simplest form - just a single determinate flower, either terminal (Trillium grandiflorum) or axillary (Hibiscus). A monochasial cyme (uniparous) has its main axis end in a flower, with only one of the two lateral bracts giving rise to further branching; if this branching develops on one side only, coiling into a helix, it is helicoid/bostryx (Hamelia, potato), and if it alternates from side to side, also often coiling, it is scorpioid/cincinnus (Heliotropium) - when successive branches first zig-zag and then straighten into an apparently single axis, the pattern is a sympodial cyme (Solanum americanum). A simple dichasium (biparous) has its central axis end in a terminal flower, with two lateral buds then producing further growth, giving three flowers per unit (a true cyme, with the central flower the oldest), as in Jasminum; a small simple dichasium is called a cymule. A compound dichasium repeats this branching from the terminal old flower on both sides, giving seven flowers per unit (Clerodendron). A polychasial cyme (multiparous) has a central axis ending in a flower while its lateral axes branch repeatedly (Nerium).

III. Mixed inflorescence shows both racemose and cymose development together, in two forms: a thyrsus is literally a 'raceme of cymes' - an indefinite central axis bearing lateral, pedicellate simple or compound dichasial cymes (Ocimum, Anisomeles); and a verticil (verticillaster) has the main axis bearing two opposite, lateral, sessile cymes at each node, each producing further monochasial scorpioid branches so that flowers appear crowded around the node (Leonotis, Leucas). …