The Rosidae
Family Overview - The Fabales
Fabaceae - the Bean or Pea Family
Diversity:  This large, diverse (trees, shrubs, and herbs), and important (both ecologically and economically) family includes over 470 genera (arranged into about 30 tribal groups) and ca. 14,000 species, both herbaceous and - mostly - woody.  This is one of two flowering plant families that became incorporated into agricultural systems as they developed throughout the world.  Since most of the legume seed is sporophytic (embryo as opposed to endosperm), it is rich in protein and, as a result, beans provide a nutritive complement to carbohydrate derived from domesticated elements of the grass family (Poaceae/Gramineae).  Major domesticates include Glycine max (Soybean- Asian), Phaseolus vulgaris (Common Bean - American), Pisum sativum (Pea-Eurasian), and Vigna unguiculata (black-eyed pea - African).  In contrast to crop lineages, most members of the family are toxic - see Abrus precatorius and Loco Weed.  Symbiotic association of this family and the  'Rhizobia' bacteria represents another 'preadaptive' agricultural trait in that many important forage taxa, such as Medicago sativa (Alfalfa) have been domesticated from the Fabaceae.
 

Distribution:  Worldwide, but most diverse in warm, temperate areas.  With 59 genera, 288 species, and 104 infraspecific taxa in Texas, this is - in terms of species diversity - the State's third largest vascular plant family (following the Asteraceae and Poaceae).  While a bit dated (1959) and out of print, Legumes of Texas by B. L. Turner provides a useful overview of Texas beans (see the copy in lab).

Floral structure:

 Significant features:  Leaves of this family tend to be pinnately compound, but, as exemplified by the Texas State Flower, palmate compounding and - rarely - simple leaves occur.  Floral zygomorphy shows, in comparison to the Caesalpiniaceae, a more pronounced a 'papilionaceous'  or butterfly-like aspect in that the standard petal is nearly always the largest of the five petals and the 'body' of the butterfly is formed by connation of the lowest two petals to form the keel which encloses the reproductive parts.  Also, in contrast to the Caesalpiniaceae, the standard petal encloses the wing petals in the Fabaceae, i.e., it must open during anthesis before the lateral petals can expand.  This tendency for connation is also expressed by the (usually) synsepalous calyx and - often - diadelphous androecium.
 
 

Caesalpiniaceae
Fabaceae



Local Baptisia bracteata (herbaceous perennial 'wild indigo' of our open uplands - now in flower); plant, papilionaceous flower with large standard petal (uppermost) flanked by two wing petals which wrap around the keel and infructescence and dehisced fruit.
 

 
 

The Texas State flower - the bluebonnet - is produced by blue-flowered Lupinus species growing in Texas and two of these are sympatric (distribution overlap) in our part of the State, L. subcarnosus and L. texensis.  While the former tends to inhabit sandy soils and the latter is usually found in clay, they are sometimes locally sympatric. These taxa are winter annuals.  The seeds germinate in the Fall and proceed to produce a basal rosette of palmately compound leaves that grows during the Winter and early Spring.  Photosynthate accumulated during this period is then invested in a reproductive effort, a racemose inflorescence.  This carries key characters to allow distinction between the two local species.  As indicated below, the infloresence of L. texensis tends to show a whitish tip and this feature allows species determination from a distance in that the inflorescences of L. subcarnonus lack the whitish inflorescence tip.  This feature of L. texensis is quite conspicuous in rare instances where, via a genetic mutation, a plant shows fasciated inflorescences.  Also, Lupinus flowers differ from those of a 'typical' bean in that the lateral wing petals enclose the keel.  This 'combined' keel is narrow and sharply 'keeled' in L. texensis, whereas the wing petals of S. subcarnosus are inflated to produce a 'cheeky' configuration on close inspection.  Only one of the 170 Lupinus species growing in North America is endemic to Texas.

Texas Bluebonnet - Lupinus texensis
inflorescence
fasciated 
flower
infructescence

Texas Bluebonnet - Lupinus subcarnosus

inflorescence
plants
flower
fruits

In flower now - vetches (Vicia), several species
 

More information on the Fabaceae


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