BOT 360F - Families of Vascular Plants 

Inflorescence typology

spikes and racemes - panicle and corymbs - cyme and umbels - head (1) - head (2) - head (3)

The inflorescence morphology observed in Ontario flowering plants (cf. diagrams below, showing a further, simplified selection) is a subset of that seen worldwide, and does not include such unusual forms as that seen in figs, where the flowers are inside a hollow receptacle (a synconium or hypanthodium). Families such as the Araceae are characterized by specialized spikes (spadices) that are each associated with a single, large bract, or spathe. The Apiceae almost universally produce simple or compound umbels. Most other families tend to be quite varied in the inflorescence types that they produce.

Inflorescences are classified as monotelic or polytelic according to whether they terminate in a flower (monotelic), or not, i.e. the inflorescence apex continues producing flowers (polytelic). Note in the diagrams below the way in which some of the types are in compound, being made up of several branches, each of which conforms to that type (e.g. compound umbel). Moreover, other types that are commonly recognized, like the panicle, can be seen as being made up of several racemes.

Inflorescences typically arise, like flowers, in the axils of leaves or bracts. Exceptionally, in some tropical species (and a few temperate ones; examine the inflorescences of Tilia, for example), inflorescences are attached to leaves (they are epiphyllous). An even rarer condition is that of cauliflory. In Cercis and Theobroma this is the result of the development of axillary inflorescence meristems that get covered over as the woody stem on which they occur increases in diameter. In the cannonball tree Couroupita guianensis, however, the inflorescence meristems arise from the cambium of the trunk. The development of other unusual inflorescence positions found in still other tropical species (e.g. in the Flacourtiaceae and Moraceae) have yet to be investigated.

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| What are plant families? | How do we distinguish them? | How and why do we study them? | Selected vascular plant families of Ontario | Reading List | Course outline |

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Please send your comments to tim.dickinson@utoronto.ca; last updated 20-Nov-2011