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Last Update 06/03/08

Botany 101

Flower Branches, Clusters, and Inflorences

Single Flower - one flower borne at the end of an elongated stalk or branch of the main axis of the plant, as in tulip and Magnolia grandiflora (southern magnolia). [The peduncle is the stalk which bears the single flower at the top (and is also the main stem or axis of a flower cluster). The pedicel is the stalk of an individual flower in a cluster.]

Cluster - three or more flowers gathered closely together in simple or branched groups to increase their conspicuousness, such as in Pentas spp. (pentas), Ligustrum japonicum (ligustrum), Pyracantha coccinea (firethorn), Mangifera indica (mango), and Dianthus barbatus (sweet William).

 

Inflorescence - general term for the arrangement of flowers or groups of flowers on a plant. There is great diversity in this arrangement among different types of plants, but they generally remain characteristic for a particular type and may be useful in identifying species. There are two main types of inflorescences, each of which is further subdivided; they are the racemose type and the cymose type. 

      Racemose Inflorescences - the axis of the inflorescence continues to grow (it is an indeterminate inflorescence) and the flowers are borne in the axes of the reduced leaves or bracts, with the oldest flowers at the base and the newest flowers near the growing tip.

o        Raceme - flowers on short pedicels of about equal length along the main axis, as in Antirrhinum majus (snapdragon) and Allamanda cathartica (allamanda).

o        Panicle - compound raceme (the branches have branches), with individual flowers replaced by simple racemes, as in Lagerstroemia indica (crape myrtle) and Murraya paniculata (orange jessamine).

o        Spike - like a raceme, but flowers lack pedicels and are sessile or almost sessile. Examples are Acalypha wilkesiana (copperleaf) and Callistemon spp. (bottlebrush).

o        Spadix - type of spike; a fleshy axis bearing the sessile, generally fleshy flowers close together, commonly surrounded and partially enclosed by a spathe . Examples are Zantedeschia aethiopica (calla) and Anthurium spp. (anthurium).

o        Catkin - spike which normally produces only staminate or pistillate flowers (see next chapter), and at maturity falls away as a unit. Examples are Betula nigra (river birch) and Quercus spp. (oaks).

o        Corymb - pedicels of older flowers longer than those of younger flowers, which brings all of them to nearly the same level. Pedicels come from different points on the main peduncle, giving the inflorescence a rather flat-topped or convex look with the outside flowers opening first. Examples are Iberis spp. (candytuft) and Ixora coccinea (ixora).

o        Umbel - short axis which causes pedicels to appear to arise from a common point (umbrella-shaped). This gives the inflorescence a knob-like look. The outer flowers open first. Examples are Anethum graveolens (dill) and Crinum spp. (crinum lily).

 

o        Head - similar to umbels, but sessile flowers are very close together. Heads may be globular or almost spherical as in Cephalanthus occidentalis (buttonbush) and Trifolium hybridum (alsike clover). What popularly passes for a "flower" in the Compositae (Asteraceae) is really an inflorescence with many small, true flowers, such as in Helianthus annuus (sunflower). Ray flowers form a fringe of radiating irregular, asymmetrical flowers (see chapter 8) on the edge of the head. Disk flowers cover the remainder of the head and are regular, symmetrical, and usually less showy. Heads may also have flowers which are all irregular with no differentiation into rays and disks.

o        Involucre - cluster or whorl of bracts or leaves directly under a flower or a cluster of flowers which is often conspicuous. They are often found under umbels and heads. Examples are Helianthus annuus (sunflower) and the cups of acorns in Quercus spp. (oaks).

      Cymose Inflorescences - Upward growth of the floral axis is stopped early by the development of a terminal flower. The first flower to open (the oldest) is at the tip; with younger flowers appearing lower down on the axis. The floral axis ceases to elongate after the first flower opens, and is therefore a determinate inflorescence.

o        Cyme - one terminal flower and two or more side flowers coming from the end of the axis. Examples are Plumeria spp. (frangipani) and Solanum seaforthianum (Brazilian nightshade).

o        Scorpioid cyme - floral axis curves over, carrying the flowers along the top of the curve, as in Heliotropium spp. (heliotrope).

o        Fascicle - flowers are very closely crowded on almost the same plane (in a tight bundle or group), as in Dianthus barbatus (sweet William).

Flower Positions

Terminal - flowers or clusters of flowers are carried on the ends of the axis or branches, as in Magnolia grandiflora (southern magnolia) and Nerium oleander (oleander).

Axillary - flowers or clusters of flowers arise at the junction of the stem or axis and the leaf, as in Catharanthus roseus (periwinkle), Callicarpa americana (beautyberry), and Hibiscus rosa-sinensis (hibiscus).

Some plants, such as Ixora coccinea (ixora), have both terminal and axillary flowers.

Source: Botany Handbook for Florida, Revised Edition, Kathleen C. Ruppert, January 1999 -- This document is copyrighted by the University of Florida, Institute of Food and Agricultural Sciences (UF/IFAS) for the people of the State of Florida. UF/IFAS retains all rights under all conventions, but permits free reproduction by all agents and offices of the Cooperative Extension Service and the people of the State of Florida. Permission is granted to others to use these materials in part or in full for educational purposes, provided that full credit is given to the UF/IFAS, citing the publication, its source, and date of publication.

 

 
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