Lab 2: Vegetative Characters

Objectives for this lab: learn the different root types learn to recognize and name different stem modifications learn to recognize and interpret simple and compound leaves become familiar with leaf shapes, bases, apices, margins, arrangements, forms, and textures and the terms that describe these features learn to recognize different growth forms--herbs, vines, trees, shrubs learn to recognize vegetative features such as thorns, spines, prickles, tendrils examine and learn to recognize different types of trichomes (plant hairs) practice keying with a key that uses vegetative characters

This lab deals with characters of the vegetative parts of a plant--roots, stems, twigs, and leaves.

Most items have a visual link, but some do not. This topic is covered fully in Vascular Plant Taxonomy by Walters and Keil .

ROOTS

Tap root--main root enlarging and growing downward
Fibrous roots--thin, thread-like roots, usually without a primary root present
Adventitious root--root growing from something other than root tissue, e.g. stem, etc.
Tuberous root---root enlarged for storage of food reserves, eg. sweet potato
Aerial root--adventitious root produced above ground, often for climbing

STEM ANATOMY

Bud--A compressed, undeveloped shoot. Buds may be lateral or terminal.
Node--point on the stem where leaf or bud is borne. The space between two nodes is an internode
Leaf scar--mark left on the stem where a leaf was attached
Bud scale scar--mark on the stem where a bud scale was attached. When the terminal bud sprouts and its scales fall off, growth rings are formed. The portion of a stem between two sets of growth rings indicates one season's growth.
Pith--the spongey tissue in the center of a stem or twig. Pith can be solid, chambered, or diaphragmmed.
Lenticel--a "breathing pore" in the skin or bark of a stem.

STEM MODIFICATIONS

Tuber--underground stem enlarged for storage of food--has nodes (unlike tuberous root)
Rhizome--underground stem, often has buds which sprout to form new shoots
Stolon--aboveground stem, has buds which sprout to form new shoots
Bulb--underground stem with fleshy leaves which store food, e.g. onion
Corm--solid, fleshy underground stem with papery leaves, e.g. Gladiolus, water chestnut

GROWTH FORM

Herb--no woody tissue
Shrub--woody, several stems from the base, less than about 25' tall
Tree--woody, usually one main stem, usually more than 25 ' tall
Vine--woody or herbaceous, stem climbing or twining

DURATION

Annual--plant which lives for one year or season, reproduces, and then dies
Biennial--plant which lives for two years or seasons, reproduces, and then dies
Perennial--plant which lives for several to many years or seasons. Perennials may be woody, with stems that persist aboveground over the winter, or they may be herbaceous, with stems that die back to the ground each year.
Evergreen-having leaves which persist for two or more seasons. Broadleaf evergreens usually have thick, leathery leaves.
Deciduous--having leaves which die and fall in the cold or the dry season.

PARTS OF A LEAF and NODE

Petiole--the stalk of a leaf; a leaf without a petiole is sessile
Blade--the flat, expanded portion of the leaf
Stipule--flat, often leaf-like flap below a leaf. Not all leaves have stipules. Stipules can be highly modified into tendrils, spines, scales, etc. Do not confuse a stipule with the
Axillary bud--the bud in the axil--the angle between the leaf and the stem.
Helpful Hint: Remember to look for stipules below the petiole and an axillary bud above the petiole.

LEAF ARRANGEMENT

Alternate--leaves arranged one per node
Opposite--leaves arranged two per node
Whorled--arranged two or more per node
Fascicled--leaves grouped in small, tight bundles, eg., pine needles bundled into clusters of 2 or 3

SIMPLE AND COMPOUND LEAVES

Simple--the blade is all in one piece, though it may be lobed, toothed, etc.

Compound--the blade is divided all the way to the midrib (rachis) into two or more pieces.
Once pinnately compound--leaflets arranged along one undivided main axis.  A leaf is even pinnately compound (paripinnate) if the leaflets are in pairs with none left over (as in the linked image.)  A leaf is odd pinnately compound (imparipinnate) if the leaflets are in all in pairs except one left over at the tip.
Twice pinnately compound--main axis (rachis) with two or more branches and the leaflets arranged along the branches. The branch divisions are primary leaflets and the ultimate divisions are secondary leaflets. There can also be thrice-pinnately compound leaves,etc.
Palmately compound--leaflets all arising from one point at the base of the leaf.

VENATION

Pinnate--with a main midvein and secondary veins arising from it at intervals
Palmate--with the main veins all arising from one point at the base of the leaf.
Parallel--with all the main veins parallel (usually also parallel to the sides of the leaf.)
Dichotomous--with each vein branching in two again and again (e.g. Ginkgo)

LOBING

Pinnately lobed--with the lobes arising along the length of the mid-line of the leaf.
Palmately lobed--with the lobes all arising from one point at the base of the leaf

LEAF SHAPES

Ovate--egg-shaped with the larger end at the bottom
Elliptic--shaped like an ellipse, tapered at both ends and with curved sides.
Oblong--tapered to both ends, but with the sides more or less parallel
Lanceolate--shaped like the tip of a lance, broadest at the base and tapered to a long point
Linear--very long and thin, with the sides parallel (In this photo, the grass-like leaves are linear; they belong to the pink-flowered plant)
Orbicular--nearly circular in outline
Cordate--heart-shaped with the wide part at the bottom
Hastate--with two basal lobes that point straight out
Sagittate--with two basal lobes that point backwards (toward the petiole)
Peltate--with the petiole attached to the center of the underside of the blade
Perfoliate--with the petiole appearing to run through the center of the leaf
Terete--circular in cross-section. (The example shown is from a succulent plant)  
 

APICES AND BASES

Acute--forming an angle of less than 90 degrees
Obtuse--forming an angle of more than 90 degrees. (In this image, the terminal lobe of each 3-lobed leaf is obtuse)
Acuminate--with a long, drawn-out taper (often with concave sides)
Rounded--just what you'd think
Cuneate--wedge-shaped
Cordate--shaped like the two lobes of a heart
Mucronate--with a tiny, usually stiff, point (mucro)
Truncate--cut straight across
Retuse--with a tiny notch taken out of the margin.
Oblique/Inequilateral--with the two halves of the base not equal in size or not meeting the petiole at the same point.
Decurrent--a leaf is decurrent if its tissue runs down the stem from the point of attachment. This is usually in the form of thin wings

MARGINS

Entire--smooth, with no teeth or lobes 
Serrate--with sharp, forward-pointing teeth
Doubly serrate--with teeth which have smaller teeth on them
Serrulate--with very tiny sharp teeth
Dentate--with teeth which point outwards
Crenate--with low, rounded scallop-like teeth
Undulate--waving up and down
Revolute--turned under
Crisped--curled tightly (e.g. parsley)
Spinose--with stiff points
Lobed, parted, divided, cut, etc.--A number of terms describe the various degrees of lobing. Different sources use the terms in different ways. Lobed is usually the least divided and pinnatifid or palmatifid usually the most--cut almost all the way to the midrib.

CLIMBING PLANTS

Twining--the stem wraps around an object for support (e.g. Morning Glory)
Tendrils--modified shoots, petioles, leaves or stipules coil around the support (e.g. Vetch)
Aerial roots---small roots, often with sucker-like tips (e.g. Virginia Creeper or Poison Ivy)

ARMATURE

Thorns--modified stems; have stem-like vasculature (e.g. Honey Locust)
Spines--modified leaves, stipules, or bud scales (e.g. Cactus)
Prickles--outgrowths of the epidermis, can be easily snapped off (e.g. Dewberry or Rose)

TEXTURE

Succulent--swollen and juicy.  Eg., cactus stems and leaves of some plants.  Here is an extreme example of succulent leaves.
Coriaceous--stiff and leathery
Herbaceous--thin and leaf-like.  (May be applied to many different sorts of parts, such as sepals, etc.)
Membranous--thin and flexible, like a membrane. (In this photo, the bracts below the flowers)
Scarious--stiff, dry, and somewhat transparent or scaly, often yellowish, whitish, or brownish in color rather than green

PLANT HAIRS and TERMS TO DESCRIBE SURFACES

Simple hairs-- straight and unbranched
Stellate hairs--shaped like stars.  The rays may be free or fused
Glandular hairs--topped with a gland or swollen and gland-like.  You may also see stalked glands--glands with stalks stiffer than hairs
Branched hairs--the main hair has side branches (look at the hairs on the midrib of the leaf)
Plumose hair or bristle--the main hair has side hairs (the smaller side hairs are just visible on each big hair)
Scale--a thin, flat structure (like a fish scale), often attached in the center
Glaucous--glabrous and with a coating of wax
Ciliate--with short hairs around the margin
Pilose--with long, soft, spreading hairs.  Here is another example.
Pubescent--with short, soft hairs  (This term is sometimes incorrectly used to refer to having hairs of any sort)
Hispid--with stiff, spreading hairs.  Here is another example (look at the hairs along the veins)
Strigose--with rather stiff, appressed hairs
Scabrous--rough or sandpapery, with very short, stiff hairs or projections (Examine the close up shots of the leaves and stem)
Tomentose--with a dense, soft coat of hairs that is hard to see through, e.g., underside of mustang grape leaves
Arachnose--with long, tangled, cobweb-like hairs
Gland-dotted-- covered with scattered glands. These usually look greasy, or like little drops of yellow or dark oil.  Glandular punctate--with the scattered glands in the bottoms of little pits. (Look at the surface of the whitish bracts below the flowers)

Return to the Table of Contents for the Lab
Return to the Botany 301 Homepage
Go on to the next lesson

last updated  28 January 2010  by MDR