Miscellaneous etceteras about roots, stems, and leaves
(or, roots from which to branch out in your study of plant anatomy. There’s a pun or two – take ‘em or leave ‘em. OK, ok, it’s three puns).
Roots:
Root system – that part of a plant, called “roots”, located “below” the stem/leaf part (the shoot system).
Primary root – the first root to develop in the embryo.
Secondary root – any and all branches off of the primary root.
Fibrous root system – secondary roots are ~ equal in diameter to the primary root. (ex. Grasses).
Taproot system – secondary roots are smaller diameter than the primary root (ex. Carrot).
Specialized roots – roots that are different in structure and/or function than the “typical” root.
Food-storage roots – all roots store some foods, but some take this to extremes. Think carrots.
Water-storage roots – as with food storage, some take this to extremes; like the calabazilla plant
and its 160 lb. underground water tank.
Adventitious roots – roots that arise from a plant structure other than the root system (like from
stems…). Often used in climbing and in asexual reproduction.
Propagative roots – roots whose primary function is asexual (= vegetative) reproduction.
Pneumatophores – roots of swamp plants that grow up, out of the water, in order for the root
system to breathe. Cypress “knees”, long believed to be
pneumatophores, may not be (no evidence….).
Aerial roots – any of a variety of roots that grow in open air. May or may not reach the ground.
Contractile roots – as these lose food and/or water, and thus contract, they pull the plant further
into the ground. Often pull bulbs deeper year to year.
Prop roots – aerial roots that assist in holding up a stem (corn, banyan trees).
Buttress roots – like prop roots, but less “aerial” – look like extensions of tree trunk (fig tree).
Parasitic roots – penetrate vascular tissues of host plants to get the goodies. Mistletoe,…anyone?
Root relationships (mutualistic):
Mycorrhizae – most seed plants have fungi associated with their roots. These fungi grow both
on and in roots, as far in as the endodermis. Fungi gain food/shelter,
while roots gain increased absorptive function.
Root nodules – growths which contain nitrogen-fixing bacteria. Very important, as this is the
ONLY mechanism by which nitrogen gas (N2) in incorporated into
compounds available to the rest of the life on the planet…. Root
nodules are found in peas, beans, and other legumes.
Stems:
A “stem” is the part of the shoot system from which leaves arise. Usually the major function is holding the
leaves up, but many types of stems are modified for different functions…..
Erect stems – any and all stems that stand upright on their own, without climbing.
Creeping stems – grow horizontally on top of the ground, and are also called “runners”. Runners often
function in asexual reproduction by growing adventitious roots and eventually
disconnecting from the parent plant. Ex. Strawberries.
Rhizomes – horizontal stems that grow below ground; usually reproductive (like runners). Ex. Day lilies
Stolons – grow below ground, often not horizontally; often mistaken for roots. Often have swellings
that store large amounts of food. These swellings are called “tubers”, and make
nice French fries.
Bulbs – very short underground stems, surrounded by numerous fleshy (food storage) leaves, and with
adventitious roots growing from the base. Onions, tulips, lilies……
Corms – like bulbs, only different. The stem itself stores food and has only thin, papery leaves around
it. Crocus and gladiolus.
Cladophylls – flattened, green stems that basically think they’re leaves. Don’t be fooled – they’re stems.
Prickly-pear cactus is a great example.
Climbing stems – any of a variety of stems modified for climbing-type growth. These may be the main
stem (like morning glories) or branches from the main stem called “tendrils” (like
grapes). Not to be confused with adventitious roots used for climbing (like poison
ivy).
Thorns – stems modified as defensive weapons. If you trod on fallen honey locust, it often makes no
difference whether or not you’re wearing shoes. Such thorns also do not go well
with tires. Don’t confuse thorns with spines (= leaves) or prickles (= epidermis);
though such anatomical distinction has little bearing on choice of expletive once
you’re pricked (or thorned, or spined….).
Suckers – stems which grow upwards from propagative roots.
Leaves:
A “leaf” is a botanical solar panel, derived from a single axillary bud on a stem. As with roots and stems, there
are many variations on the theme. Some (like spines…) no longer serve as solar panels at all.
Leaf vocabulary:
Petiole – the stalk attaching the leaf to the stem.
Blade – the flat, light-collecting part of the leaf.
Veins – vascular bundles within a leaf.
Simple – a leaf with a single-piece blade.
Compound – a leaf with a blade divided into leaflets (compound leaves have a single axillary bud at the
stem, and the leaflets have no such buds).
Pinnate – leaflets arranged in pairs along a central extension of the petiole. Superficially
resemble fern fronds. Ex. walnut, hickory.
Bipinnate – leaflets sub-divided again, pinnately.
Palmate – leaflets arise from the same point at the end of the petiole. Ex. poison ivy,
hemp.
note: “pinnate” and “palmate” also refer to the pattern of venation within leaf blades.
Deciduous – a plant that drops/re-grows leaves seasonally.
Abscission – the process by which deciduous leaves are shed.
Specialized leaves:
Needles – as in pine needles; still function in photosynthesis, but modified to reduce water loss.
Spines – no longer photosynthetic, function in protection. Ex. cactus.
Tendrils – modified for climbing growth, like peas. (Yes, it’s the same name as the stem. How would
you know if a tendril were a stem or a leaf?).
Storage leaves – thickened or otherwise modified to store water or food. Ex. cactus, aloe.
Reproductive leaves – specialized for asexual reproduction; grow “baby” plants which then fall off.
Floral leaves (bracts) – leaves specialized to advertise the presence of flowers. Ex. poinsettia.
Insect-trapping leaves – self explanatory function. Flytraps, pitcher plants, sundews…Venus’ kidtrap.
Note: these plants are autotrophic (photosynthetic), but grow in nitrogenpoor soils. They eat animals for the nitrogen, not for energy.
And of course sepals, petals, stamens, and carpals…which you already know all about.