FALL SEMESTER, 1997

Laboratory of Biochemical Ecology, University of Kentucky, Lexington, KY 40506, garose@pop.uky.edu

INTRODUCTION

The trees of Kentucky can be divided into two groups: gymnosperms and angiosperms. The Gymnosperms produce "naked seeds" borne on an exposed surfaces of a seed-bearing cone. In a pine, for example, the seeds rest on the exposed scales of the mature cone. These plants do not produce showy flowers nor seeds that are protected, enclosed within fruit. Also known as conifers, they are taken to be "evergreen" because nearly all members retain their foliage for more than one year.

PLANT NAMES

How do trees get their name? For the purpose of identification, every plant needs to have a unique name, but problems results from name changes and the not-so-surprising fact that the same plant is known by differenct names from different locations. The potential for confusion and error is real and too often realized.

To bring some order to this chaotic situation, a system of naming has been established that is based on Latin and employs two elements to create a system known as binomial nomenclature. The final term designates the name of the species. A species is a fundamental unit that refers to a group that act as an independent, interbreed population. Species with similar characteristics, resulting from the fact that they share many common genes, are grouped together into a genus (genera is the plural). The latin binomial must be written in italics, with the genus being capitalized while the species is lower case.

There are a number of palo verdes that grow in Arizona. This group of trees share many characteristics and they are grouped together into a genus known as Cercidium. Close scrutiny of these trees reveals populations with distinct characteristics-genes that they do no share with other palo verdes. This uniqueness creates a separate species for these trees. Thus, the foothill palo verde whose latin binomial is Cercidium microphyllum (the species name denotes the minute foliage) is a distinct group within the genus of palo verde plants. No matter how many common names this tree may have (and it will have more than one), everyone knows what plant is being talked about when you use the name Cercidium microphyllum.

N.B. Plant samples that are submitted but fail to observe the rules of a correctly written latin binomial will not be graded.

The angiosperms of Kentucky comprise the largest assemblage of trees. This word is derived from the Greek and refers to a "vessel" and sperma or "seed". Thus, angiosperms were given their name because they possess seed-bearing vessels, ie. the carpels bearing the ovules.

These plants are characterized by their showy, often fragrant flowers and the protection of their seeds by enclosure within substantial structures that are the fruit. The foliage is typically deciduous for it is lost at the end of each growing season. Gymnosperms, by contrast, have much more persistent foliage.

FLOWERS

An angiosperm flower is made of four floral components:

• The sepals which protect the flower, are typically greeen, but can be colored.
• The petal, a showy part of the flower which is typically brightly colored, scented, and highly conspicuous.
• The carpel, it houses the the ovary which in turn protects the female sex cells or ovules.
• The stamen, it produces the pollen grains that will ultimately develop into the mature male sex cell-the mature pollen grain.

A complete flower is one that has all floral components-sepal, petal, carpel, and stamen.

Most angiosperm flowers are perfect-each flower contains both a carpel and a stamen.

Other angiosperms are imperfect, that is they have flowers that contain only one of the floral parts that will house the sex cells. If they are capable of creating the female sex cells, theses carpellate flowers are distinct from the staminate flowers which are able to produce the male sex cells.

Sometimes, the carpellate are found on one plant while other, separate plants house the staminate flowers. This arrangement create a dioecious plant (from the Greek for two houses).

When the carpellate and staminate flowers are found on the same plant it is monoecious plant (one house).

THINK ABOUT THIS:

THE FLOWERS OF MONOECIOUS OR DIOECIOUS PLANTS ARE NEVER PEFECT.

A PERFECT FLOWER CAN BE COMPLETE OR INCOMPLETE BUT AN IMPERFECT FLOWER CANNOT BE COMPLETE.

FLORAL ORGANIZATION

The flowers occur at the end of a flower stalk or peduncle. In the simplest arrangement, the peduncle ends in a single flower but it can also support a cluster of flowers known as an inflorescence. The individual flowers of the inflorescence are attached by a pedicle.

A flower is a determinate shoot bearing sporophylls (organs bearing sporangia). A sporangium is a spore-bearing (ie. the haploid cells) organ. In the case of the flower, they are the stamens and carpels.

Flowers can be constructed so that the stamen and perianth are connected to the receptacle below the ovary. This is a superior flower because the ovary is above or superior to the other floral parts.

If the stamens and perianth emanate from the top of the ovary, it is an inferior flower.

left to right: cylindrical cyme, flat-topped cyme, spike (individual flowers are connected directly to the penduncle), catkin or ament (as in Betula).

left to right: raceme (the individual flowers are connected to the penduncle by a pedicle), panicle (multiple flowers are connected to the penduncle by pedicles), globose head

corymb (flowers alternate along the penduncle), umbel (individual flowers emanate from a common point), flat-topped head.

A FINAL BUT TRENCHANT NOTE ON THE FLOWER:

• In the angiosperms, FLOWERS are the characteristic reproductive structures. A flower is regarded by botanists as a specialized shoot, some parts of which are directly involved in reproduction, others of which are only indirectly concerned with reproductive activity. Some of these floral organs are leaflike in development and structure, whereas others have the developmental and anatomical characteristics of stems.
• Flowers develop from buds, as do vegetative shoots. Some buds produce only flowers (lilac, tulip, morning-glory, and poplar)-these are true flower buds; other buds produce both flowers and leaves (buckeye and apple), and are responsible for the increase in the lengths of stems.
• Flowers differ from vegetative shoots in that there is virtually no elongation of their internodes, as a result of which floral organs are bunched together and are not distributed at obvious intervals along the floral axis.
• Flower growth is determinate; that is, no further apical growth occurs after the floral parts have been formed, whereas apical growth of the vegetative shoot is indeterminate. Flowers also differ from vegetative shoots in that buds normally do not develop in the axils of floral organs as they do in the axils of green leaves of vegetative twigs. The parts of a flower develop as lateral protuberances of a bud's terminal portion in much the same way as do foliage leaves. The lowermost floral organs usually develop first followed in order by the more apically situated parts, those nearest the tip of the bud enlarging last.