The Asteridae is the last and most derived dicot subclass. The following unifying characters apply to about 80% of the species, and most species will have at least 2 or 3 of these: corolla fused, stamens epipetalous, stamens as many as or  fewer than the corolla lobes, ovary bicarpellate.

1. Asclepias - Asclepiadaceae - Gentianales:

OBTAIN a flower and compare with the wall chart an p. 275 in W&K. NOTE the perianth of 5 sepals and 5 petals. Above these is another series of perianth parts, the CORONA, which encloses the gynoecium at its base and extends outward as five corona HOODS. Some species also have HORNS projecting from the hoods.

This flower differs from all others that we have examined in that the androecium is not immediately evident. Five stamens are fused to the gynoecium, forming a single structure known as the GYNOSTEGIUM, the central "column" of the flower. The enlarged terminal portion of this column is the stigma with five anthers adnate around its periphery. Five small, dark CORPUSCULA (glands) should be evident around the upper rim of the gynostegium. Place your teasing needle beneath one of these dark structures and gently lift it away from the gynostegium. The structure you remove, the POLLINARIUM, should be similar to that depicted on the wall chart and in fig. 14-12 in W&K. NOTE TRANSLATORARMS and POLLINIA.

Next, EXAMINE the ovaries of this species by removing the outer corona wall beneath the enlarged tip of the gynostegium. NOTE that the ovaries are united ONLY by their stigmas. The fruit will be a follicle. The seeds are comose.

FLORAL FORMULA_____________________
SKETCH the flower, noting gynostegium, hoods, horns, and glands.
SKETCH the polliniarium, noting gland and translator arms.  
 

2. Physostegia or Stachys - Lamiaceae (Labiatae) - Lamiales:

EXAMINE a flower and CONSTRUCT a floral formula.
Use more mature flowers (calyx only) for examination of the fruits. What is the fruit type?____________________
FLORAL FORMULA: _____________________________________
DIAGRAM the PERIANTH, ANDROECIUM, and GYNOECIUM of your flower:
NOTE characteristics of this distinctive family: sympetalous, BILABIATE corolla; DIDYNAMOUS stamens (outer pair slightly longer than inner pair); four-lobed ovary with GYNOBASIC STYLE; and SQUARE STEMS with OPPOSITE LEAVES.  
 

3. Asteraceae (Compositae) - Asterales:

This is a huge family. Recognition characters include: Flowers arranged in involucrate heads, 5-merous, sympetalous; calyx reduced to a pappus (or none); gynoecium bicarpellate, inferior; fruit an achene.  This is a high-level pattern of variatin in the family.  It is usually involved in the initial couplets of any key to genera.


Inflorescences in the Asteraceae fall into three general categories:

1. RADIATE = BOTH ray florets and disc florets present
2. LIGULATE = ONLY ligulate florets present
3. DISCOID = ONLY disc florets present

3a. Helianthus sp. - Asteraceae (Compositae) - Asterales:

Become acquainted with key characteristics of this family by examining this large inflorescence. OBTAIN 1/2 of a Helianthus head and compare with the wall chart. BE SURE that you can recognize all labelled structures in the Helianthus material.
Also, compare your material to the following genus description from Correll and Johnston (Manual of the Vascular Plants of Texas):
"....HEADS usually borne singly [on] terminal PEDUNCLES; INVOLUCRES usually saucer-shaped to hemispheric; RECEPTACLE plane to convex, CHAFFY throughout; PALES folded around the disc achenes; RAY FLOWERS uniseriate, usually pistillate but always infertile, the yellow rays 3-toothed apically; disc ACHENES laterally compressed; PAPPUS usually of two elongated awns over the thinner shoulders of the achene..."
DIAGRAM both a ray floret and a disk floret:
 
 

3b. Pyrrhopappus sp.:

EXAMINE your Pyrrhopappus inflorescence. Note the LIGULATE inflorescence and pappus of CAPILLARY BRISTLES which will allow the fruits to be wind-dispersed.
DRAW a ligulate floret:

3c. Cirsium sp.

TAKE a few flowers. COMPARE the flowers against the key to genera of the Asteraceae. NOTE: long styles, lack of ligulate corollas, pappus type, and NAKED or HAIRY receptacle.
DIAGRAM a flower:
 
 
COMPARE your three samples of Asteraceae with regard to receptacle shape (flat/ concave/ convex/ conical...), position of the phyllaries (imbricate/ valvate), presence or absence of ray, disc, and ligulate florets, the sex of each flower type present (perfect/ pistillate/ sterile), pappus type (awn/ capillary bristle/ plumose bristle, etc...), presence or absence of chaff, etc.

Additional Families

Oleaceae--Ours trees and shrubs. Ex: Fraxinus (ash) and Ligustrum (a common landscape plant here)
Solanaceae--Large family; many species have an alkaloid chemistry. Ex: Solanum (potato, tomato, eggplant, nightshade), Capsicum (pepper), and Nicotiana (tobacco)
Bignoniaceae--Ours woody; flowers zygomorphic. Ex: Campsis (trumpet creeper)
Verbenaceae--Square stems, +/- zygomorphic flowers, terminal style. Ex: Verbena (vervain) and Lantana (calico bush)
Scrophulariaceae--Square stems, zygomorphic flowers, terminal style and capsular fruit. Ex: Castilleja (Indian paintbrush) and Agalinis (false foxglove)

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last updated 24 July 2007 by MDR