BS/PLS 210
Fall semester, 1997
WEB PAGE ASSIGNMENT:A 01
Laboratory of Biochemical Ecology, University of Kentucky, Lexington, KY 40506, garose@pop.uky.edu
INTRODUCTION
The trees of Arizona 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).
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.
The angiosperms of Arizona comprise the largest assemblage of trees. 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:
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.
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.
FRUITS
When the ovules, housed within the ovary, of the flower are fertilized by the mature pollen grain, they grow into the seeds while the ovary matures into the fruit. Thus, a fruit is a matured ovary that may or may not retain aged floral remnants, that protects the internal seeds. It can be confusing. Remember that the carpel houses the ovary which in turn supports the ovules.
A fruit is considered a simple fruit if it forms from a single ovary consisting of one carpel or the fusion of numerous carpels.
A compound fruit results when many separate carpels function in creating the fruit.
COMPOUND FRUIT
In an aggregate fruit, multiple carpels contained within a single flower, aggregate together to form a discrete fruit. Thus, an aggregate fruit is an aggregation of carpels (but from only one flower).
A multiple fruit is one where multiple carpels, derived from a number of flowers, fuse to form the fruit. Arizona sycamore, Platanus wrightii is an example of a tree that produces a multiple fruit.
SIMPLE FRUIT
Simple fruits are best placed into one of two groups: fleshy or dry fruits. It is best to think about a fleshy fruit as being divisible into 3 sections:
FLESHY FRUIT
DRUPE
When the fruit has a thin exocarp and a fleshy mesocarp that covers a hard and stony pit (endocarp) that protects the seed. Prune, cherry, peach and plum are examples of edible drupes. Do not confuse the stony pit (endocarp) with the seed that is housed within. Usually only one carpel containing one ovule.
BERRY
When the fruit has both a soft and fleshy mesocarp and endocarp and the seeds are dispersed throughout the fruit.
A drupe is a simple fruit (derived from a single pistil) with one seed. When a berry has but one seed, it can be difficult to distinguish between a fruit in which the seed is protected by hard, external tissues (endocarp) that are not part of the seed (drupe) and a fruit where all of the hard, internal tissues are of the seed (berry).
POME
In this fruit, the mesocarp is fleshy but the exocarp surrounding the seeds is papery or cartilaginous. An apple or a pear are examples. A pome is interesting in that part of the tissues that support the ovary (receptacle) are carried over into and becomes part of the mature, edible fruit.
DRY FRUIT
Most fruits are dry but they can be grouped into two assemblages: those that split open at maturity (dehiscent) and those that do not (indehiscent). Once again, this can be problematic since an immature fruit will not open, and thereby appears indehiscent, until it is fully developed.
DEHISCENT
LEGUME
Many important Arizonan trees such as the palo verdes are legumes. A legume is formed from a simple carpel ( no chambers or sections within the fruit) that opens along two sutures that form in the wall of the fruit. Many ovules exist in the ovary that forms a legume, so there are numerous seeds in this fruit.
FOLLICLE
Botanically, a follicle is similar to a legume in that it forms from a single carpel, and contains multipe seeds, but the fruit opens along a single suture
CAPSULE
A capsule is created from a compound carpel. It dehisces or opens in many different ways..
Most dry, dehiscent fruit are capsules. If more than one section or chamber exists within the fruit and it is dry and dehiscent-it must be a capsule.
INDEHISCENT
ACHENE
A single seed exists within the fruit and it rests mostly free within the fruit cavity except for a small appendage that attaches it to the fruit wall.
SAMARA
Modification of an achene in which the ovary wall is expanded to create a wing. This is the fruit of ash (Fraxinus) and elm (Ulmus).
NUT
These fruit superficially resemble achenes but they have a hard, stony fruit wall and they are derived from a compound ovary.
A nut can be difficult to identify. Typically, a nut is enclosed with a husk which may be papery, leafy, woody, or spiny. The outer wall of the nut is hard as it is made of fibrous sclerids. What makes matters worse, is that abortion can lead to the development of only a single ovule-even though many ovules originally existed in the ovary.
Arizona walnut has a fruit that looks very much like a nut and is called a nut, but the seed is actually enclosed in a stony pit and the outer, green husk, while not fleshy is the exocarp of a drupe.
A horsechestnut also superficially appears to be a nut, but this is not the case. The fruit opens at maturity and no nut is dehiscent. What appears to be a husk is actually the outer ovary wall of a capsule.
Recognizing individual fruit groupings is not easy; it takes time and patience to acquire skill and accuracy.
LEAVES
The leaf of an angiosperm is its food-producing organ. Tiny bodies within the leaf called chloroplasts, are storehouses of chlorophyll molecules that trap the energy of the sun for use in synthesizing carbohydrates for the plant. The bulk of the leaf is the broad, flat portion or blade which is attached to the stem by the petiole. The petiole attaches to the twig at the node.
The underside of the leaf blade has numerous small openings for gas exchange known as stomata (stomates).
The nodal area can also contain stipules, small appendages that are modified leaves and occur paired and attached to the petiole.
ATTACHMENT
Leaves can be attached to the branch in three different ways:
ORGANIZATION
Angiosperms typically possess a simple leaf consisting of a single leaf blade. In some instances, however, they have a compound leaf which is made of leaflets.
Compound leaves can be:
palmately compound-multiple leaflets arise from a common place on the petiole.
pinnately compound-the leaflets arise from multiple points along the petiole. Typically, the leaflet is sessile, it arises directly from the petiole. This leaf arrangement occurs in Arizona walnut, Juglans major.
Arizona walnut, Juglans major
bi-pinnately compound-occasionally, the petiole is subdivided by a structure called a rachis which is actually an extension of the petiole. Individual leaflets are attached directly to the rachis which, in turn, is connect to a common petiole. This leaf arrangement is found in various Arizona mesquites, Prosopis.
Arizona mesquite, Prosopis julifloria
Leaves can be distinguished from leaflets in two ways:
SHAPE, BASE, APEX, AND MARGIN
SHAPE:
1-needle-like, 2-scale-like, 3-linear (long and narrow, with parallel sides), 4-oblong (approximately 3x longer than wide with sides that are largely parallel), 5-lanceolate (shaped like a lance), 6-inverted lanceolate, 7-ovate (shaped like a longitudinal section through an egg), 8-obovate, 9-elliptical, 10-oval, 11-circular, and 12-crenate (kidney-shaped).
13-cordate (heart shaped), 14-triangular, 15-diamond-shaped, and 16-spalulate (shaped like a spatula).
BASE
First row (left to right): cuneate (wedged-shaped), acute, cordate (heart-shaped), inequilateral
Second row (left to right): obtuse, rounded, flattened, auriculate (ear-like).
APEX:
First row (left to right) acuminate, acute, mucronate (bristle-tipped), cuspidate (spine-tipped)
Second row (left to right): obtuse, rounded, truncate (flattened), and emarginate tched).
MARGIN:
(left to right) rovolute, entire, repand (undulates), sinuate (strongly undulate)
(left to right): crenate, serrate, dentate, doubly serrate
(left to right): doubly crenate, lobed, cleft, parted
TWIGS
A twig is that part of a tree which supports the buds and leaves and is an extension of a branch. The leaves, arranged on the twig as previously described, are supported by the petiole which is attached to the twig at the node.
Buds are formed in the angular zone formed by the petiole and the stem. Since this is an axil, such buds are known as axillary buds. These buds contain the following season's branches or flowers. A twig also has a terminal bud at the apex which generates tissues responsible for twig increase in length.
Angiosperms are largely a deciduous assemblage. They lose their foliage annually. When the leaf and petiole fall from the twig in the autumn, a leaf scar is created at the node. Careful examination of this scar reveals small bundle scars which form from tissues that connect into the leaf from the branch to provide water and move food materials from the leaf.
The size and shape of the leaf and bundle scars are distinct for each tree and a vaulable clue for their identification when the leaves have fallen.
DESCRIPTIVE BOTANICAL TERMS
pubescent-hairy
hirsute-hairy
glabrous -smooth
imbricate-overlapping, like shingles of a roof
globose-spherical in shape
GYMNOSPERMS
Members of the Coniferales or conifers are the economically most important and widespread group of gymnosperms. They are prevalent at high altitutes and in the cold regions of the temperate zone. Almost all are arborescent and their wood is used widely for timber and as a source for pulp (fiber) for paper-making and related industrial uses.
These plants are typically pyrimidal and the massive main axis (trunk or bole) is the primary source for merchantible timber. They are able to gain impressive heights, often exceeding 300 feet in the giant sequoia, and redwood forests of California and in sitka spruce and douglas-fir that reside in the temperate rain forest of the Olympic peninsula.
The growth in girth that can produce individuals with a diameter at breast height of more than 30 feet . Conifers are perennial since their vegetative tissues are persistent and last many years. The western hemlock of the Olympic peninsula live to 500 years, the sitka spruce to 600, but the other two dominant trees of this temperate rain forest: western red cedar and douglas-fir can survive a century. Far longer-lived are the redwoods and giant sequoia, but the longevity record is held by bristlecone pine which can reach 5,000 years in age.
Conifer leaf morphology is varied but nearly always small and simple in shape that ranges from needlelike structures (several cm in length) to closely appressed scales that extend only a few mm. The leaves are borne on short shoots that persists for several seasons. Only in a few genera such as larch, Larix is the foliage truly deciduous.
Stems:
PINE
The pines (Pinus) are the most abundant genus of conifers in Arizona. These plants are characterized by straight, unbranched, cylindrical trunks and foliage that is needle-like and rounded. All pines bear 1-5 needles that are arranged in groups and bundled together to form a fascicle. The usually pendent cone is made of hard, woody material, often armored with a sharp prickle. Two seeds, often papery winged, are borne on each scale.
SPRUCE
The spruces (Picea) typically possess a sharp-pointed, pyramidal crown and branches that descend in a pattern of whorls. The needles are 4-sided or flattened, spirally arranged around the twig, and are attached to the twig without a stalk. They exhibit stomata on their upper-side, and are supported by a wooden peg or sterigmata. The cones are soft, almost papery, and concentrated at the apex of the tree.
CEDAR
The cedars (Cupressus) produce a scale-like leaf that can form flat, horizontally feathery sprays. The fruit is a spherical structure made of interlocking scales that are shield-shaped and attached to the stalk of the cone at its lower surface, raised structures can project from these scales.
JUNIPER
The junipers (Juniperus) are generally small and highly aromatic trees that have needle- or awl-like juvenile foliage, but can be scale-like at maturity. The fruit is an indehiscent cone that is superficiallly berry-like in appearance, succulent, and often highly aromatic.
HEMLOCK
The hemlocks (Tsuga) are tall, broadly pyramidal, often with drooping pendent branch es. The foliage is spirally arranged, linear, and solitary. Needles are flattened, and possess a small, terminal stalk that attaches to the twig. Dual bands of conspicuously-colored (whitish) stomata occur on the underside. The immature cones are small, pendent, closed, soft and deeply green but at maturity then open, and become brown and papery.
DOUGLAS-FIR
Douglas fir (Pseudotsuga menziesii) is a conifer distinct enough to merit its own genus. The foliage is linear, solitary, flattened, and spirally arranged. Distinctive for its pendent, papery cone that bears three-lobed bracts that protude from the cone. The winter buds are long (0.25"), conical and sharply pointed with a lustrous brown coloration.
FIR
The true firs (Abies) produce spirally-arranged, linear, sessile foliage that is typically flat and blunt. The needles bear stomata on the underside, but they are not as conspicuous as in Tsuga. The cones are soft like Picea but always erect.