The development of partial florescences in the main florescence is highly variable and influenced by the environment where the plants grow (Cremers & Sell, 1986); however, in Amaranthaceae, the development of the partial florescence and that of solitary flowers in the florescence seem to be genetically determined for different groups.
Accordingly, florescences in the Amaranthaceae family may consist of:
1) Fully developed partial florescences bearing three or more flowers (Fig.
2) Partial florescences reduced to one or a few fertile flowers having prophylls with more or less modified axillary productions (Fig.
3) No partial florescences but solitary flowers having prophylls with no axillary productions (Fig.
The Flowering Unit in Species with Florescences Bearing a Solitary Flower
When the FU lacks a paracladial zone and is only composed of the main florescence, if the florescences comprise partial florescences arranged along an axis, then the FU is a spike-like thyrse, such as occurs with Amaranthus, Digera, Chamissoa Kunth, Pleuropterantha Franch.
The shape and hair density of the prophylls and the sterile flowers in the partial florescences contribute to fruit dissemination by the wind (Cavaco, 1962; Engler, 1964).
Differences among the models of synflorescences present in Amaranthaceae may be explained in terms of the following processes: development of the florescence prophyllar bud; reduction of flower number in the florescences; reduction of the number of partial florescences in the florescences; shortening of internodes of the florescences; shortening of the basal internode of the partial florescences; shortening of the basal internode (peduncle) of the florescences; reduction of the paraclade number; reduction of the branching degree of the paraclades; shortening of the internodes of the main axis and of the paraclades; reduction of the number of leaves along the main axis and in each paraclade.
In his new system, largely based on inflorescence characters, Cavaco (1962) analyzes the flower and inflorescence morphology in Amaranthaceae and explains variations observed in the structure of partial florescences (which he calls "partial" or "elementary" inflorescences).
It may be one flower, one florescence, or a more complex branch system (Rua, 1999).
In the flowering unit we recognize the main florescence and the enrichment zone (or paracladial zone), which is composed of a variable number of paraclades (paraclades of the flowering unit, Pc Fig.