The traditional separation between Amaranthaceae sensu stricto and the  Chenopodiaceae was essentially arbitrary. For instance, the Chenopodiaceae had stamens that were usually distinct whereas those in the Amaranthaceae varied from slightly to completely connate; the Chenopodiaceae had greenish, membranous or fleshy tepals whereas the Amaranthaceae has white, pink, or red dry, papery tepals.  Judd et al. cite several references that support the combination of the two families into a single family.  It is unfortunate for us that the family usually encountered in Utah is the one with the younger name, but life is like that at times.

Morphology. 
Habit: The Amaranthaceae are herbs or shrubs (often low shrubs in our port of the world), not trees; some species are succulent throughout, others simply have succulent leaves, others are not succulent at all.  The vascular bundles are usually in concentric rings. The plastids of the sieve elements have a proteinaceous ring, but not a proteinaceous crystal core.

Leaves are alternate or opposite, simple, without stipules.

Inflorescences are determinate, terminal and/or axillary.  

Flowers are usually bisexual, radially symmetric, often associated with bracts.  The perianth usually has 3-5 distinct to slightly connate tepals, 

The androecium has 3-5 stamens with separate to more or less connate filaments. The pollen grains are 7 to many porate.

The gynoecium consists of 2-3 connate carpels, usually with a superior ovary and basal placentation and 1-3 style branches.  The number of ovules is 1-few.

The fruit is an achene, a utricle, or a capsule but the distinctive feature is the curved to spiral embryo.  

Chemistry Betalains (nitrogen containing pigments) are present and some species have C₄ photosynthesis. 

Importance
There are a few economically useful  species in the family, such as Beta vulgaris, Spinacia oleracea, and some species of Amaranthus and Chenopodium. There are also many weedy species of Amaranthus and Chenopodium, which represent positive economic benefit if you are in the weed-killing business, negative if you are farming.  There are also some ornamental species in the family, mostly in the old Amaranthaceae part of the family.  

In Utah, the family is of great ecological importance. Much of the desert portion of the state is dominated by species of Atriplex and the highly saline areas support Salicornia and Allenrolfea. Then there are also such nasties as Salsola.  

Amaranthus seedling

Amaranthus retroflexus


Celosia argentea

 
Ptilotus exaltatus

Atriplex falcata (habitat)

Atriplex canescens

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