The sixth and final dicot subclass. Unifying
characters: fused corolla, stamens epipetalous, stamens fewer than the
corolla lobes, bicarpellate gynoecium. (About 80% will have at least
2 or 3 of these features.)
1. Asclepiadaceae--Herbs, many with milky sap,
flowers highly modified, corona present, made up of hoods,
which may also have horns. Gynoecium bicarpellate, the carpels
united only above. Stamens fused to stigma, creating gynostegium.
Each half-anther produces a pollinium joined to a pollinium of neighboring
anther by agland (corpusculum) and translator arms. Fruit is a follicle,
often with comose seeds. Ex.: Asclepias (Milkweed).
2. Lamiaceae (Labiatae)--Herbs with square stems
and opposite leaves, often aromatic. Flowers bilabiate, stamens
2 or 2+2 (didynamous). Style gynobasic, arising from among 4 lobes of bicarpellate
ovary. Fruit cluster of nutlets (cocci). Ex.: Mentha, Salvia,
Stachys, many herbs--basil, rosemary, lavender, oregano, marjoram,
thyme, sage, horehound, etc.
3. Asteraceae (Compositae)--Large, diverse family with flowers arranged in heads (capitula) on a common receptacle, entire head subtended by involucral bracts or phyllaries, individual flowers subtended by pales=chaff. Each flower with a pappus instead of calyx; calyx of bristles, scales, awns, etc. or absent. Corolla fused, stamens 5, synantherous; ovary inferior, bicarpellate, fruit an achene. Heads of three kinds:
a. Radiate--both disk and ray florets.Disk florets regular, usually perfect and fertile; ray florets zygomorphic, with ligule, perfect, pistillate, or neuter.
b. Discoid--only disk florets--regular and usually all perfect
c. Ligulate--only ligulate florets--zygomorphic, with ligule, usually all perfect.
This is all we have time for. Don't forget some other important Asteridae families:
Scrophulariaceae--opp. leaves, bilabiate flowers, style terminal, fruit a capsuleReturn to the Asteridae lab exercise
Verbenaceae--opp leaves, square stems, flowers +/- zygo., style terminal, nutlets
Boraginaceae--alt. leaves, regular flowers, style gynobasic, nutlets
Polemoniaceae--regular flowers, ovary tricarpellate, capsules
Caprifoliaceae--opp. leaves, no stipules, zygo or actino. flowers, drupe/berry/capsule
Rubiaceae--opp. leaves, stipules, reg. flowers actino, capsule, schizocarp, etc.
last updated Sept. 28, 2000 by MDR