BOTANY 328 - LABORATORY 2 - FLORAL STRUCTURE
11 September 1997
 TAXA EXAMINED
 

1. Portulaca grandiflora (Portulacaceae) - Purslane, Rose-Moss (images)

 Floral structure: Calyx: 2 sepals Corolla: 5 petals Androecium: numerous stamens Gynoecium: 5 carpels (determined from stigma lobes) fused

 A typical Dicot

 2. Allium schoenoprasum (Liliaceae) - Chives (Allium images - Liliacaeae)

Floral structure: Calyx: 3 sepals Corolla: 3 petals (sepals 'petaloid' - 6 'tepals' with calyx evident by relative position only) Androecium: 6 stamens Gynoecium: 3 carpels (ovary septa) fused

 A typical Monocot

 
3. Helianthus annuus - wild type (Asteraceae) - Sunflower (Helianthus images)

Cluster of small flowers to form a 'flower-like' inflorescence (capitulum) that marks this largest of dicot families.  Capitula take several forms, although all types found in the family are usually subtended by a cluster of bracts known as phyllaries.  This type - the radiate inflorescence - features fertile flowers ('disc' florets) with actinomorphic (radially symmetrical) corollas at the center and flowers ('ray' florets) that are non-functional reproductively around the margin.  A close look into the corolla tube of a ray floret shows no androecium or style and a reduced ovary that will not set fruit.  The disc florets (these from the domesticated type), on the other hand, are fully equipped (note fused anthers that form a tube [just above the corolla lobes] through which the style emerges [two yellow, coiled structures above the brown anther tube].

Floral structure - disc floret:  The calyx is represented by two 'awns' placed on top of the ovary near the point of ovary attachment of the corolla tube.  Highly specialized and variable in this family, and often absent, the term 'calyx' is replaced by the term 'pappus' for this family.  The tubular corolla is terminated by 5 lobes (5 petals involved), 5 stamens are attached to the corolla (epipetalous) and, while there is only a single locule and seed in the ovary, the two stigma lobes indicate a syncarpous gynoecium made up of two carpels.

Floral structure - ray floret: The corolla here is also sympetalous (5 petals fused), but the product of this fusion is a straplike or 'ligulate' structure that, within the context of the entire infloresence, serves an 'attraction' function.  It is a zygomorphic corolla (not radially symmetrical).

4. Croton capitatus (Euphorbiaceae) - Dove Weed (images)

Representing a large and economically important dicot family, dove weed produces unisexual flowers ('imperfect') with staminate and pistillate flowers present on an individual plant (= a monoecious species - species with individual plants producing only either staminate or pistillage flowers are dioecious)

Floral structure:  Calyx reduced and variable, no corolla, stamens variables (7 - 12) for staminate flowers, pistillate flowers with a tricarpellate (1 seed per locule), syncarpous gynoecium.
 

5.  Passiflora incarnata (Passifloraceae) - Granadilla, Passion Flower (images)
 
Floral structure:  An unusual flower that shows a deviation from the CA/CO/A/G sequence via 'insertion' of the 'fringed' whorle known as a 'corona'.  See the family description for more detail.

6. Capsicum annuum (Solanaceae) - Chile Pepper

Floral structure:  Calyx of 5 sepals (symsepalous), corolla of 5 fused petals, stamens 5 and EPIPETALOUS, gynoecium syncarpous (two carpels).  See fruit sections showing basic bicarpellate condition (bananna pepper) and derived septum (bell pepper).

7. Senna alata (Fabaceae - Leguminosae s.l.) - 'Senna' (images)

Floral structure:  The interpretation offered for this flower (reduced synsepalous calyx with doubled corolla) is was incorrect.  The perianth is 10-parted with the lower 5 (falling easily) petaloid (yellow) representing the calyx and the 5 just above these representing the corolla.  The androecium has 10 stamens with differing anther sizes, this evidently relating to function of the pollen (food for vectors vs. reproduction).  The gynoecium, a marker for this large and important family, is unicarpellate.  Senna relatives are often treated as a distinct family.

8. Catharanthus roseus (Apocynaceae) - Periwinkle (images)

Floral structure:  calyx of 5, awn-like sepals, corolla of 5 petals fused to form a tubular base (side view) and a 5-lobed 'limb'.  Androecium of 5, epipetalous stamens that tend to clasp the stigma (see this in a relative, Vinca).  Gynoecium of two carpels that are fused to form a common style/stigma but separate at the base.  Thus, at maturity, each flower tends to produce two unicarpellate fruits.

9. Dendrobium sp. (Orchidaceae) - Dendrobium (images)

Floral structure:  3 sepals and 3 petals with one of the 3 petals modified in various ways to form a 'lip' or labellum thereby producing a zygomorphic flower.  Unusual feature that marks this largest monocot family:  reproductive whorles fused to form a single structure - the column or gynandrium and the pollen 'packaged' (pollinia) for vector transport.  See family description for more detail. 

10. Asclepias curassavica (Asclepiadaceae) - Milkweed (images)

Floral structure:  Calyx of 5 sepals and corolla of 5 petals (reflexed, red).  Similar to the Passifloraceae in that coronal structures (hood and horn) are present and the Orchidaceae in that the reproductive whorles are fused to form a single structure and anther contents are 'packaged' into pollinia.  See family description for more detail.

11. Hibiscus sp. (Malvaceae)

Floral structure:  A family of local economic importance in that Cotton is a member.  Perianth, often subtended by a calyx-like whorle of bracts (epicalyx), of 5 sepals and petals and an androecium of numerious stamens that are fused to form a 'filament tube' around the style.  Carpel number ranges from 5 to numerous but always syncarpous and, in Hibiscus, 5 carpels as indicated by 5 'capitate' stigmas.


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