Plants & Human Affairs - Plant Structures
Cherries.wmf (7140 bytes) Plants & Human Affairs (BIOL106)  -  Stephen G. Saupe, Ph.D.; Biology Department, College of St. Benedict/St. John's University, Collegeville, MN 56321;;

Overview of Plant Structures

 I. Major Organs

  • flower – produce fruits/seeds
  • roots – anchor, store nutrients, underground, positively gravitropic
  • leaves – photosynthesis, attached to stem, has a bud at its base
  • stems – supports leaves, flowers and fruits; usually negatively gravitropic, with buds

There is often no clear anatomical distinction between leaf and stem. The crown is the junction of the root and stem. A shoot is a stem with leaves.

II. Plant habit.

  • herb - no woody tissue, soft stems
  • shrub - multiple stems, woody
  • tree – single stem, woody (oaks, maples)
  • succulent – very fleshy, juicy stem (cactus)
  • vine – stem that climbs or trails, requires support. Lianas are woody vines
  • forb - non-grass herbaceous plants.

III. Life span/Duration:

  • annual – completes life cycle in a single year.
  • biennial – completes life cycle in two years; the first year typically as rosette (like carrot) and the second year it bolts (produces a flowering stalk that grows quickly)
  • perennial – lives more than two seasons
  • evergreen – keeps its leaves year-round
  • deciduous – looses its leaves at the end of the growing season

Trees are shrubs are perennials. Annual plants can usually herbaceous.

IV. Roots

  • tap – one main root, carrot
  • fibrous – many roots, no one root is dominant, like grasses
  • adventitious – a root that develops from a part of the plant other than another root, like the prop roots of maize, or the tendrils of ivy
  • root hairs – tiny outgrowths of the epidermis designed to absorb water and minerals

V. Stems

A. Stem features:

  • node – region to which a leaf is attached
  • internode – region between nodes
  • bud – found at base of leaf, immature shoot system
  • axillary (or lateral) bud – bud at base of leaf, along stem
  • terminal bud – bud at end of stem
  • bud scales – protective covering over bud, modified leaves
  • bud scale scar – scar left on stem where the terminal bud scales fell off
  • leaf scar – scar left on stem where leaf detached
  • lenticel – areas on stem for gas exchange
  • vascular bundle scar – in leaf scar, where vascular bundle went into leaf

B. Specialized Types

  • rhizome (ginger)
  • stolon (strawberry)
  • bulb (onion)
  • corm (gladiolus)
  • tuber (potato)

C. Meristems – Growth in plants is restricted to certain regions called meristems. These can be found at the tips of roots and stems (apical meristems) and are responsible for growth in length. The vascular cambium, which produces vascular tissue (xylem and phloem) is found in the stem and is responsible for growth in width.

VI. Leaves

A. Parts

  • blade – main photosynthetic part
  • petiole – fancy term for the leaf stalk
  • stipules – appendage are base of petiole in some leaves. Stipules can be glandular, leafy, spiny, or scale-like. In many cases, the stipules fall off shortly after the leaf expands. Many plants completely lack stipules.

B. Leaf structure: The leaf blade may be all one section or broken up into smaller sections (called leaflets)

C. Leaf Arrangement – Leaves may be found only at the base of the plant (basal, rosette, as in dandelion) or along the stem or some combination.

D. Venation. This refers to the pattern of the main veins which can be pinnate (like a feather), palmate (like the fingers on your hand), parallel.

E. Specialized Leaves – leaves may be modified in a variety of different ways. For example, the leaves of carnivorous plants are modified into traps. Tendrils are common in vines and used for support. Tendrils can actually be derived from modified leaves or stems

VII. Flowers.

A. Floral Parts. The flower is the key feature of angiosperms. It produces the male and female GAMETES (sex cells). Evolutionarily, the flower is a short shoot (branch). Thus, it is made of modified leaves and stem. The "leafy" parts are readily apparent in the sterile outer parts; it is more difficult to see the "leafy" origin of the fertile, inner parts

B. Stem Axis.

  • Pedicel - is the stalk beneath an individual flower
  • Receptacle - is the swollen or enlarged terminal portion of the pedicel to which the other floral organs are attached.

C. Sepals - outermost layer of floral parts, collectively called the calyx. Sterile, "leafy", often green (photosynthetic), but may be colored or petaloid. The sepals enclose the flower in the bud stage and protect developing inner parts.

D. Petals - interior to the sepals, collectively called the corolla. Note spelling - don't spell like the objects used to propel a bicycle. Usually colored, larger than sepals, delicate. Primary function - attract pollinators. Pollination - transferring pollen from stamens to carpels. Note - pollination is different than fertilization!

E. Stamens - collectively called the androecium; male reproductive organ; interior to petals. function is to produce pollen (male gametophyte). Comprised of two sections: (a) anther - microsporangium or pollen sac, usually 2 or 4 chambered, in which pollen is produced; (b) filament - stalk that attaches anther to receptacle.

F. Carpels - collectively gynoecium. Female reproductive organ. Inner most floral structure. Their function is to produce the female gametophyte, which in turn produces the egg.

    The carpels are evolutionarily modified leaves that have rolled and differentiated into: (a) stigma - pollen receptive surface; (b) style - stalk; and (c) ovary - enlarged basal portion that contains one or more ovules (which house the female gametophyte).

    The term pistil is used to refer to the structure that is differentiated into stigma, style and ovary. Remember, a pistil is not a weapon!

G. The typical flower.
    The structure of a "typical" flower is described above. However, there are few plants with "typical" flowers. In fact, finding a flower that looks like the "textbook diagrams" can be somewhat difficult. Most flowers are modified, to a greater or lesser extent, from the basic pattern.

IX. References:

  • Harris, J.G. & M. W. Harris. 1994. Plant Identification Terminology: An Illustrated Glossary. Spring Lake Publ, Spring Lake, UT.
  • Cronquist, A. 1988. Evolution and Classification of Flowering Plants. 2nd edn. New York Botanical Garden, NY.
  • Zomlefer, W. Guide to Flowering Plant Families. This book has an excellent illustrated glossary

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Last updated:  08/25/2003 / � Copyright  by SG Saupe / URL:
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