[Rosids: Fabids]
Fabaceae (=Leguminosae: beans)
Snow peas, showing typical flowers and fruit.
On-line sources
U. Wisconsin Plant Systematics: Fabaceae
Plants of Guam on-line: Caesalpinia; Canavalia; Cynometra; Intsia; Leucaena; Derris; Sophora; etc.
The Fabaceae is a huge family with three distinct subfamilies (see technical key below). Beans are in the Papilionoideae; this subfamily includes all the beans we eat, including peas, lentils, and soybeans (tofu), as well as peanuts. This is the subfamily that has the "typical" legume flowers. The Mimosoideae have pompom-like flowers; it includes trees such as tangantangan (Leucaena leucocephala) and herbs such as sleeping grass (Mimosa). The Caesalpinoideae includes such well-known trees as the flame tree and ifit, as well as food crop plants such as tamarind. All these plants have root nodules with nitrogen fixing bacteria, making them good pioneer species in poor soils (that's why forestry plants Acacia, e.g., on the trail to Tarzan Falls), or good for "green manure" (that's why farmers in cooler climates plant clover to allow their fields to fallow).
Winged bean flower and pod.
Characteristics of the subfamily Papilionoideae
Flowers are distinctive in having one large, erect petal (sometimes called the banner), plus four arranged in a group around the carpel and stamens (the wings and keel). The fruit in all the subfamilies is a pod; at maturity the fruit is dry and splits along two edges. The name refers to an imagined resemblance to a butterfly.
Picture of dissected pea flower.
Key to subfamilies*
1. Flowers actinomorphic, small, often congested in heads, calyx tubular;
stamens 5-many, exserted.......................................
Mimosoideae.
1. Flowers slightly to markedly zygomorphic; often large and showy,
rarely congested in heads; sepals 5, imbricate; stamens 10 or
less, free, or united.
.................................................................
2
2. Flowers barely zygomorphic; stamens free...................Caesalpinoideae
2. Flowers markedly zygomorphic, papilionoid, with 2 petals connate
to form the keel; 2 lateral petals (wings); 1 larger petal,
often erect or reflexed and with unique pattern or coloration
(rarely reduced), the
banner or standard; stamens usually
connate in bundles, often 9
together and 1 free........ Papilionoideae
[*actinomorphic = radially symmetrical, can be cut into equal halves along
several planes; zygomorphic = bilaterally symmetrical, can be cut into equal
halves only along one plane; connate = joined]
Source of the key: Stone, Flora of Guam. Micronesica 6.
C. Lobban 11/24/00