Pinnate This term describes a compound leaf which has a row of leaflets on each side of the rachis. There are two types of pinnate leaves, paripinnate and imparipinnate. Paripinnate
Shapes of leaf bases
It can sometimes be difficult to categorise leaf bases as there are graduations between each main base type. A leaf base may, for instance, be somewhere between auriculate and hastate (eg Philodendron species). Only experience with the bases will enable you to confidently identify those which are not typical.
1 Other morphological features of leaves
There are other morphological features which make recognition of plant species easier and permit correct and accurate identification.
Leaf venation refers to the direction in which the veins of leaves run in relation to the main vein (mid-rib) and the margin.
Always look further than the venation when determining whether a genus is a monocotyledon or a dicotyledon. The fact that some species of Eucalyptus and Melaleuca have parallel venation (which are both dicotyledons) does not mean that they are automatically classified as monocotyledons.
The way in individual leaves are physically attached to the stem is another characteristic useful in the identification of species.
This refers to the actual arrangement of leaves on the stem, regardless of how they are attached.
This is an important aspect of leaf description. You should understand the terms in the following list and be able to apply them to any given leaf. They are very useful for identification. They are not examinable.
Glabrous - smooth, without hairs. Example: Camellia japonica
Pubescent - downy, having short, fine soft hairs
Tomentose - having short, dense hairs, usually matted together to form a felt - like surface; having woolly hairs. Example: Cerastium tomentosum
Villous - having long, soft hairs
Hirsute - covered by coarse hairs
Hispid - covered with short, stiff hairs
Scabrous - having a rough surface., eg Celtis australis
Glaucous - having a blue colour
Flower shapes and inflorescences
This section deals with the various shapes of flowers and the way these flowers can be arranged as a group to form an inflorescence.
When a flower shape is discussed, it is the shape of the petals and/or sepals (the perianth) which constitutes a flower shape. However, because there are also many flowers which do not fit exactly into any one of the flower shapes, it is quite acceptable to combine more than one shape name to describe a specific flower shape.
If the flower does not have distinct sepals and petals (perhaps only one whorl) then it is the shape of that petal like structure that is described.
As you are now aware, the arrangement and shape of the perianth segments (usually the petals) within the one flower structure gives rise to a range of different shapes. Knowing the flower shapes makes identification of some plant species easier and can be used to classify plants into plant families. For example, all flowers which are in family Fabaceae, sub - fam. Faboideae, have a papilionate flower shape. Again, labiate flowers are usually in family Lamiaceae.
The stalk of a single flower is known as the pedicel.
Shaped like a tube, the sides are parallel or nearly so, eg Cuphea ignea (cigar flower).
Having a slender cylindrical lower part and opening out flat at the mouth, eg Phlox spp, Plumbago spp. The sides of the lower part of floral tube are nearly parallel.
Funnel - shaped; petal lobes may turn back at the top, but not as flat as salverform flowers. The sides of the floral tubes are not parallel gradually widening from the base to the top of the flower, eg Petunia x hybrida, Hibiscus rosa - sinensis.
Bell - shaped; base of flower is more rounded than funnelform flowers. Flowers normally hang down, eg Abutilon x hybridum (Chinese lantern).
Wheel - shaped with a short tube at base and spreading at the mouth; petals free from each other, eg Hibbertia spp. (guinea flower), Tibouchina spp, Lagerstroemia indica.
Star - shaped, petals usually free from each other, usually 4, 5 or 6 petals, eg Hemerocallis spp. (day lily), Trachelospermum jasminoides.
Having one or more petals forming a lip, eg Prostanthera spp, Salvia splendens. Also bilabiate – having two lips, eg Westringia fruticosa. Flowers with labiate or bilabiate shape are typical of members of family Lamiaceae.
Irregularly shaped flower with lowest petal spurred or modified into a rounded sac.
Corolla tube often with a sac - like bulge on one side, eg Grevillea spp., Nemanthus spp.
Shaped like the toe of a slipper, eg Paphiopedilum spp. (slipper orchid), Calceolaria. Flower with large bulge on one side.
Shaped like the wings of a butterfly, eg Lathyrus (sweet pea), Wisteria; made up of three distinct petal types:
Typical of members of family Fabaceae, sub - fam. Faboideae.
Flowers shaped like a shallow open bowl, saucer, or crater of an extinct volcano, eg Papaver spp. (poppy), roses (single).
Cup - shaped, and open at the top; more curved at the bottom than funnelform and deeper than crateriform; petals not curving out as in campanulate flowers, eg Cobaea scandens (cup and saucer vine), Tulipa spp.
Urn - shaped, narrow at the mouth and wider below, similar to cyathiform but nipped in towards the top; these flowers are often quite small, eg Erica carnea (spring heath), Epacaris spp, Arbutus unedo, Pieris japonica spp.
Petals spreading like many rays from a ‘centre’ of reproductive structures; more petals present than rotate or stellate flowers (eg Mesembryanthemum (pigface) Lampranthus). This term is often incorrectly used to describe the inflorescence of members of family Asteraceae.
Having showy stamens
With these types of flowers, we are describing what we see (which are the stamens) rather than the shape of the perianth. It does not mean that these flowers do not have all the parts of a ‘typical’ flower, it is just that it is the stamens which are obvious and showy. There are two types of flowers with showy stamens.
Flwers with many conspicuous, often brightly coloured and showy stamens; sepals and petals present but may be small and inconspicuous (eg Melaleuca, Callistemon).
Fowers with many conspicuous, often brightly coloured and showy stamens; flowers have no petals when the stamens are mature (eg Eucalyptus). The petals have been modified into a protective structure which is shed as the stamens expand and the flower matures.
An inflorescence is defined as a group of flowers borne on one stalk or stem. This inflorescence stalk is called the peduncle. The arrangement of individual flowers on a peduncle gives rise to several different inflorescences.
Some inflorescences can be very difficult to determine—in fact, some may be a combination of two inflorescence types. For example, the inflorescence of Lantana species is an umbellate spike. You may find it easier to identify some inflorescences by studying them before all the flowers are opened, or if the flowers have opened, shake the inflorescence gently and turn it upside down.
You must always locate the flowers that have opened first; that is, the oldest flowers in the inflorescence. This will help to determine the inflorescence type. You will note that the individual flowers on some inflorescence diagrams are numbered. Number 1 = oldest flower, or flower formed and opened first, 2 = second formed and opening flower, 3 = third formed and opening flower—and so on to the youngest flower on the inflorescence.
Types of inflorescence
There are three main types of inflorescence:
Solitary flower borne singly on a pedicel. They may be formed as a terminal flower or singly in the leaf axils up a stem, eg Papaver nudicaule (poppy), Westringa fruticosa.
Raceme type or indeterminate inflorescences
These are all characterised by having the oldest flower opening at the base of the inflorescence while growth is still continuing longitudinally.
A group of flowers attached to the peduncle with pedicels of about the same length; the oldest flower is at the bottom of the inflorescence and the youngest at the top, eg Salvia splendens.
A racemose inflorescence with sessile flowers (without a pedicel), eg Callistemon spp. (bottlebrush).
A branched racemose inflorescence with each whole branch being a raceme. The side branches are smaller racemes. A panicle is a compound raceme, eg Yucca spp.
A racemose inflorescence in which all the flowers are ultimately borne at the same level because the pedicels are of uneven lengths. The flowers towards the bottom of the peduncle (that is, the oldest flowers) have the longest pedicels, eg Iberis spp. (candytuft), Spiraea spp.
A racemose inflorescence in which all the pedicels are equal in length and arise at one point on the peduncle. The flowers are at the same level, eg Hippeastrum.
An inflorescence made up of small umbels arranged in a larger umbel, the peduncles are equal in length, eg fennel, parsley.
A pendulous racemose inflorescence modified for wind pollination. It is a loose spike make up of numerous sessile, usually unisexual flowers. Female catkins usually have long hairy styles and stigmas to enhance pollen interception.
A racemose inflorescence with sessile flowers on a flattened and expanded peduncle, eg Zinnia elegans.
Each inflorescence consists of two floret types
Cyme type or determinate inflorescences
These are characterised by having an inflorescence in which the terminal flower terminates the growth of that inflorescence and other flowers arise laterally below it. The oldest flowers are nearest the apex, eg Ranunculus spp. (buttercup), Tibouchina spp.
When the flower arise both sides below the terminal flower sides the inflorescence is a dichasial cyme.
When the flowers arise from one side only below the terminal flower, the inflorescence is a monochasialcyme.
2 The ‘typical’ flower
Flowers come in all shapes, sizes and colours, yet at the same time they have some features in common.
Figure 2 - A ‘typical’ flower
Arrangement of floral parts
Floral parts are inserted on the receptacle of each flower. They can either be arranged in whorls or spirally on the receptacle.
In most flowers the calyx, corolla, androecium and gynoecium are arranged in circles or whorls on the axis of the flower, eg rose, Petunia spp, Hibiscus spp.
Some flowers have the calyx, corolla, androecium and gynoecium attached at different levels in an ascending spiral, eg Magnolia spp, Ranunculus spp.
Verilənlər bazası müəlliflik hüququ ilə müdafiə olunur ©azrefs.org 2016