Taxonomy of Flowering Plants - LECTURE NOTES
Hugh D. Wilson

Vegetative Morphology II

The Leaf 

leaf 

Structural features of a simple leaf, as depicted above include the stalk (petiole) which is usually attached to the shoot at the node, subtending (attached beneath) the lateral meristem, and often with a distinctive basal enlargement (pulvinus).  Foliar or leaf-like appendages that are not similar to the typical photosynthetic leaf, but occur on the plant, often in association with flowers or inflorescences, are known as bracts.  When they are associated with the petiole base, often flanking it at the node, they are called stipules.  Significant indentations in the leaf blade tissue are called sinuses.

Review STRUCTURE and PHYLLOTAXY

TERMS DEALING WITH LEAF BLADE SHAPES - GENERAL (overview)

Linear - long and narrow with nearly parallel sides
Lanceolate - Lance-shaped, tapering from a broad base to an apex; much longer than wide
Oblong - long and wide with nearly parallel sides
Elliptical - football (American) shaped - a flatten circle, usually more than twice as long as wide
Ovate - egg-shaped with the broadest part toward the base (note that obovate is the reverse relative to the point of petiole attachment to the blade)
Cordate - heart shaped with a basal sinus

TERMS DEALING WITH LEAF BLADE SHAPES - BASAL LOBING (overview)

Sagittate - basal lobes pointed back toward the petiole - arrowhead shaped
Auriculate - with ear-lobe like appendages at the base
Petiolate - with a petiole (three of the overview images)
Sessile - petiole reduced - the leaf blade appears to be attached to the stem
Hastate - basal lobes pointing outward relative to the long axis of the blade

Bilateral symmetry is typical.  However, when the leaf shows asymmetry at the base this is known as an oblique leaf base
 

TERMS DEALING WITH LEAF BLADE SHAPES - LENGTH = WIDTH (overview)

Deltoid - triangular
Peltate - shield shaped with the petiole not attached at the blade margin
Reniform - kidney shaped

TERMS DEALING WITH LEAF BLADE VENATION (overview)

Dichotomous - equal bifurcation or forking, more common in ferns and gymnosperms
Palmate - the main veins radiating from the point of petiole/blade junction
Pinnate - a central 'mid-vein' or -mid-rib' with with lateral veins arising along its length
Parallel - veins running side by side without intersecting - typical of monocots
Reticulate - typical pattern of dicots with intersecting network of veins

TERMS DEALING WITH LEAF BLADE LOBING (overview)

Palmate vs. Pinnate vs. Divided (also 'parted' (almost divided) and 'pinnatifid' (pinnately parted)

TERMS DEALING WITH LEAF BLADE TIPS (overview)

Acuminate - tapering gradually to a prolonged point
Acute - ending at a point that is less than a right angle - distinct/sharp (not acuminate)
Obtuse - with a blunt or rounded tip
Cuspidate - tipped with a sharp and rigid point
Mucronate - tipped with a small, pointed extension of the mid-rib
Truncate - cut squarely across the apex
Retuse - having a shallow notch at the apex
Emarginate - also notched at the apex, mid-way between Retuse and Cordate
Cordate - a deep notch at the apex, found in an obcordate leaf

TERMS DEALING WITH LEAF BLADE MARGINS (overview)

Entire - no indentations, lobes, or teeth - smooth
Serrulate - small, marginal teeth pointing toward the blade apex
Serrate - marginal teeth pointing toward the blade apex (saw-like)
Doubly serrate - with both small and larger serrations
Dentate - marginal teeth point outward
Spinose-dentate - as above with the teeth point-tiped
Crenate - with low rounded or blunt teeth
Crenulate - with small, low rounded or blunt teeth
Undulate - a slightly wavy margin
Broadly crenate  - intermediate between undulate and sinuate
Sinuate - deeply wavy margin

TERMS DEALING WITH SURFACE FEATURES - TRICHOMES (overview)

Flowering plants produce an array of hair-like structures (trichomes) that provide 'covering' or surface characters.  Some terms applied include:

Puberulent - minutely pubescent (covered with short, soft trichomes
Stellate - with star-shaped trichomes
Tomentose - woolly in appearance, densely matted, soft trichomes
Glandular - with glands (trichomes with secretory function )
Hirsute - long shaggy trichomes, often stiff or bristly to the touch

Scabrous - thin, membranous, dry and often rough
Strigose - stiff hairs appressed and all pointing in one direction
Villous - dense covering of  long, fine, soft trichomes
Pilose - scattered covering of long, fine, soft trichomes
Glabrous - no trichomes - smooth surface

OTHER TERMS DEALING WITH SURFACE FEATURES

Glaucous - have a waxy bloom (photo)
Coriaceous - a rough, leathery texture

TERMS DEALING WITH PRODUCTS OF THE ROOT MERISTEM (overview)

As indicated above, below-ground features can be important to determine annual vs. perennial for an herbaceous sample, and also to document the presence of modified stems.  The true root system is, however, a bit bland (nodal pattern is absent) and - as a result - not a rich source of useful characters.  Terms associated with root types include:

Tap - the central or primary root that enlarges and grows downward - typical of dicots (photo)
Fibrous - thread like, often tough root system - typical of monocots (photo)
Adventitious - developing from something other than the root meristem or radical (photo)


Terminology associated with the flowering plant reproductive system (overview)

  The origin and subsequent dispersal/differentiation of the flowering plants remains a matter of some debate, as does the phylogenetic nature of the flower.  However, it appears that the flower is a highly modified shoot.  The floral appendages (sepals, petals, stamens, and carpels) therefore represent modified leaves.  The notion is fundamental to the classification system that we will be using in that archaic groups tend to show floral structures that are 'shoot-like' and more advanced or specialized elements of the angiosperms show flowers that are also highly specialized and well removed from their shoot-like origins.  All flowers tend to show a four-parted pattern of structural organization, from the base to the tip of the flower terms applied to this include:

Pedicel - stalk of an individual flower if part of an inflorescence (cluster of flowers)
Peduncle - stalk of an inflorescence or that of a solitary flower
Calyx - lower-most whorl of floral appendages (made up of sepals)
Corolla - next flora whorl or series of appendages up from the calyx (made up of petals)
Perianth - term applied to the non-reproductive floral appendages
Androecium - above the corolla and the first reproductive whorl (composed of stamens)
Androperianth - terms applied to perianth and androecium combined
Gynoecium - last of the series of appendages and positioned above the others (composed of carpels)

The flower and its products, fruit and seed, is a rich and import source of taxonomic characters and we will pick up a 'floral' vocabulary over the next two lectures.


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