Articles: BULB CHAT June 2002 PDF Print E-mail
Thursday, 26 May 2011 23:11

BULB CHAT JUNE 2002 No. 28


THE MIRACLE CLIVIA

A new Clivia has been described in the latest Bothalia. The plant is called Clivia mirabilis.

The genus Clivia now consists of 5 species, namely C. miniata, C. nobilis, C. gardenii,

C. caulescens and now also C. mirabilis. The previously known 4 species all occur in coastal and inland Afromontane forest from the Eastern Cape through KwaZulu-Natal, Swaziland and Mpumalanga to the Soutpansberg in the Northern Province. Clivia mirabilis is apparently confined to the Oorlogskloof Nature Reserve to the south of Nieuwoudtville. The area is characterized by a semi-arid Mediterranean climate with a strictly winter rainfall regime - exactly the opposite climatic conditions experienced by the other four species in the genus.

The plants are evergreen and up to 1,2 m tall. The root system is massive - up to 0,7 m in diameter and horizontally spreading. The dull green leaves are stiffly erect, strap-shaped,

O,6 - 1,2 m long and 30 - 50 mm wide. The base of the leaves are maroon flushed. The inflorescence is umbel-like and drooping. There are between 20 and 48 flowers at a time on the inflorescence. The flowers are actinomorphic, bicolored ( orange/yellow ) and tubular.

Interestingly, the drooping pedicels are orange-red when the plant is in flower and turns green when fruiting.

The question obviously arises - How could a Clivia have evolved about 8OO km away from it"s closest relative? The answer lies in the fact that there is enough evidence to suggest that at some stage in the past there were forests stretching from near the Western coast via the Cape to the Eastern parts of South Africa. Clivia mirabilis has survived the changes that have taken place by adapting the seed maturation period (much shorter) as well as the seedling and germination biology to the arid Mediterranean climate. A miracle Clivia indeed.

ROCKS AND SOILS

We often refer to substrate rock of particular soils. Soils are formed by the erosion of rock and the addition of vegetable matter. Rocks which are already the accretion of nutrient or potentially nutrient substances are obviously most likely to provide soils in which plants can grow. These are sedimentary rocks : sandstone, conglomerate, limestone and shale. Igneous rocks ( solidified from semi-molten state) are only valuable to us in that they form a base on which other soils and water can accumulate. They include granite and basalt. Much the same applies to metamorphic rocks which are rocks which have been transformed structurally or chemically by heat, pressure or chemical fluids. Depending on the chemical factor these may support very specialised soils and therefore specialised plants. Usually the plant has learnt to tolerate the chemical rather than actually to need it. Examples are gneiss, schist, slate and marble. Sand and clay are primarily measures of particle size, not of composition. Clay is a soil which can form a paste with water and hardens when dry. Dolerite, common in some of our bulb areas, is an igneous rock softer than granite, and therefore weathers more easily, contributing to soil. Sand does not form a paste with water but tends to repel ( drain ) it, but water may be trapped between the particles, at least for a time.

HOW OLD IS THE EARTH ?

According to geologists the earth is between 344O and 455O million years old. At some early stage the earth was just a molten mass at an excessively high temperature. Gradually it cooled. According to fossil records, life was already somewhat advanced 6OO million years ago taking the form of bacteria, fungi, blue-green algae and some primitive invertebrates. There is evidence of life in the sedimentary rocks formed about 2 OOO million years ago.

Geological time scale is divided into 3 Eras - The Paleozoic(oldest), Mesozoic and Cenozoic.

Each Era is divided into successively smaller units of time called Periods, Epochs and Ages.

The relative age of rocks is determined by their position in a stratigraphic sequence.

EARLY FLOWERING SPECIES.

If we ignore the Autumn-flowering hysteranthous Gladioli, the first Winter-flowering Gladiolus to flower in our pots is either Gladiolus guthriei or Gladiolus priorii. Gladiolus guthriei now includes specimens that used to be called Gladiolus odoratus. These plants flower from April to June and have up to 13 clove-scented flowers on a spike. The flowers are adapted for pollination by small, night-flying moths. Gladiolus guthriei can be seen flowering along Bains Kloof Pass as well as along Dasklip Pass, above Porterville. It also grows in profusion on the Gifberg, but here you have to walk to see it. Gladiolus priorii, previously known as Homoglossum priorii, is relatively common on granite outcrops from Saldanha Bay in the west to as far as Hermanus in the east. Flowering of these plants with their bright red flowers and long perianth tube begins in April and they could be seen flowering until July. Gladiolus priorii is adapted for pollination by sunbirds - red flower, elongated flower tube with a wide cylindrical upper part, exserted anthers and a large volume of nectar of low sugar concentration.

The first Lachenalias to start flowering in our pots would include Lachenalia bulbifera, L rubida,

L viridiflora, L congesta and L pusilla. Lachenalia bulbifera and L rubida we discussed in the previous Bulb Chat. Lachenalia viridiflora is found amongst the granite outcrops at Saldanha Bay and Vredenburg. It grows in the humus-rich shallow depressions on the granite outcrops.

L viridiflora flowers from May to July. The colour of the flowers vary from green to blue-green to turquoise. A practical point when growing Lachenalia viridiflora is to grow them in as little shade as possible. They tend to elongate very quickly when grown in shade and the inflorescence would then fall over. Lachenalia congesta is a dwarf species from the Calvinia, Sutherland and Middelpos districts. It has 2 dark green leaves with a distinctive maroon margin. The inflorescence is very dense and the small flowers are yellow to green. The flowers are scented. Lachenalia pusilla is an unusual Lachenalia. It has erect white flowers at ground level and a rosette of prostrate leaves. Lachenalia pusilla looks more like a Polyxena and to prove this affinity it tends to elongate the peduncle during the fruiting stage , similar to all

Polyxenas. Flowering time is from April to June and these small plants are found growing in sand from Nieuwoudtville to as far east as Swellendam.

From April to June many members might have a white-flowered Freesia in their pots. Although most of us might think that it is Freesia alba it certainly is not.This plant is in fact Freesia caryophyllacea. This Freesia also includes what used to be known as Freesia elimensis. The flowers are white with yellow markings, on the lowermost, or all three lower tepals. The reverse of the tepals may be flushed with purple. The traditional concept of Freesia caryophyllacea is that the leaves are prostrate, but in cultivation and in shade these plants most often develop fully erect leaves. Some specimens are highly scented while others hardly have any scent. Freesia alba flowers later - from June to September. The white flowers are nearly actinomorphic and heavily scented. Freesia alba grows on sandy or stony soils near the coast, while Freesia caryophyllacea grows on clay as well as limestone and in Renosterveld.

WORDS OF WISDOM

In a book published in 1943 the author wrote : " Though the natural environment of any plant gives valuable hints on its cultivation, it is by no means an infallible guide to that art. Even if we were to reproduce it in every detail - temperature, light, soil, water,atmospheric conditions,

plant associations - the imitation would not guarantee success " He also wrote : " There is another way in which natural environment may lead us astray. Bulbs are found in nature at almost any depth. The distance from the surface is often taken as a guide in planting, apparently on the assumption that the bulb has reached it in obedience to some inviolable law. No account is taken of landslides, silting, flooding or anything else which may have increased or decreased the thickness of the surface soil".

In the 6O years since that was published nothing has changed it's essential correctness.

PLANT NAMES

The scientific names of plants are either Latin words or words that have been latinized from some other language, most often Greek. Each species of plant has only one correct scientific name, peculiar to that species alone. This is called a binomial and consists of a generic name and a specific epithet. For example, Freesia alba is the binomial for the white Freesia discussed above, Freesia being the generic name, and alba the specific epithet. The specific epithet is therefore the second part of a binomial. It is however, never correct, to use the specific epithet alone to designate a particular species. It must always be combined with a generic name to form the binomial for that species.

Specific epithets are formed from nouns, adjectives, participles, etc. , and by combining such words with a variety of prefixes and suffixes. Every Latin or latinized noun has gender, either masculine, feminine or neuter. In most cases, each gender is indicated by a different ending.

Most nouns ending in -us are masculine, nouns ending in -a are nearly always feminine, while those ending in -um are neuter. An adjective or other modifier must agree in gender with the noun it modifies. While a noun will have only one nominative ending depending upon its gender, a modifier will often have three different endings, depending upon the gender of the word it is modifying. Thus the Latin adjective for " hairy " appears with three different endings as it modifies the nouns Gladiolus, Romulea and Vaccinium, respectively masculine, feminine and neuter : Gladiolus hirsutus, Romulea hirsuta and Vaccinium hirsutum.

The names of persons are sometimes used as specific epithets, generally to honor or commemorate the person who first discovered a particular species. In such cases the specific epithet usually has a genitive rather than a nomnative ending.

A specific epithet taken from the name of a man should be formed as follows:

1. If the name ends in any vowel except a ( e,i,o,u and also y ) the letter i is added to the end of the name, e.g. Gladiolus guthriei - named in honour of Francis Guthrie , a British botanist and mathematician who made many important plant collections in the southern Cape. Another example is Gladiolus martleyi , an autumn-flowering species named in honour of J. F. Martley , a bulb-grower who collected the Gladiolus and brought it to the attention of the botanists at Kirstenbosch in the early 193Os.

2. If the name ends in an a , the letter e is added : balansae for Mr Balansa.

3. If the name ends in a consonant, ii is added : Gladiolus priorii was named in honour of Richard Prior, a British medical doctor and amateur naturalist who collected actively in South Africa in the years 1846 to 1848. If the name ends in -er, only one i is added, which is an exeption : Gladiolus salteri - named in honour of the amateur botanist, Captain T. M. Salter who made the type collection of this Gladiolus near Springbok in 1933.

4. If a name is used as an adjective, it must agree in case and gender with the genus it modifies : Gladiolus mortonius - named after Mr Morton who sent plants of this species to Great Britain, where they were flowered and the type illustration was made. Ornithogalum dregeanum is the feminine form - named after plant collector Drege. Lachenalia barkeriana - named after Miss W. F. Barker, former Curator of the Compton Herbarium at Kirstenbosch and possibly the most knowledgeable person ever on the genus Lachenalia.

5. If a woman's name is used in the substantive form as an epithet, the ending will be the feminine genitive singular for that word : Gladiolus emiliae - named after Emily Ferguson an active plant collector in the Riversdale and Swellendam areas in the 192Os and 193Os. Another example is Gladiolus mostertiae - named in honour of Aletta Johanna Mostert, of the farm Claudskraal on the Bokkeveld escarpment near Nieuwoudtville. She sent the first recorded specimens of this species to the N.B.G. at Kirstenbosch in 192O.

In future months we will discuss some of the people that plants are named after in more detail.

We will also look at other factors which are used or taken into consideration when naming plants - colour of flowers or fruit, shape of leaf, discoverer of the species or place of discovery.

Names of plant parts are frequently used in combination with prefixes and suffixes - biflorus.

DUTHIASTRUM LINIFOLIUM

Duthiastrum is a monotypic genus. The only species is Duthiastrum linifolium. These plants grow in the north-eastern parts of the Northern Cape, as well as in the North-West Province and northern Free State. Duthiastrum is closely related to Tritonia and Sparaxis. The flowers are long-tubed and yellow. The flowers appear consecutively. Two specimens brought back from the Northern Cape by Dr John Manning in 2OOO started flowering on the 6th of April.The last flower was seen on the 11 th of June. The flowers were not hand pollinated and no seed was formed. On the 16 th of June a careful count revealed the remains of 36 flowers on the one plant and 12 on the other plant. What makes a plant flower 36 times in about 7O days?

Is it waiting for pollination to take place? Would it stop flowering if the first flower was pollinated? We know that the onset of flowering is stimulated by the length of the days. We get what is known as Short-day plants and Long-day plants. Plants that flower in the Spring are

Long-day plants - They need the lengthening of the days to start flowering. Duthiastrum must be Short-day plants, because flowering started and continued as the days were shortening.

Reliance on the perception of day length by the leaves to control and initiate flowering is called photoperiodism. There are obviously other factors which also play a roll in the initiation of flowering such as the plant hormones Gibberellins and Auxins as well as Ethylene. There are both stimulatory and inhibitory factors which play a roll here. The next question of course is whether the same factors play a roll in continuous flowering as seen in Duthiastrum.

PLANT HORMONES

Plant hormones are organic compounds made in one part of a plant and transported to another part of the plant, where they elicit a response. Plant hormones are active at small concentrations. Plant hormones and the responses that they elicit have the following characteristics :

a) Although a hormone may have some characteristic effects, it also has many other effects. That is, a single hormone can elicit many different responses.

b) The responses elicited by a hormone depend on many factors, including the presence of other hormones, the amount of hormone present, nonhormonal factors and the sensitivity of the tissue to the hormone.

c) Hormonal responses change under different conditions and in different plants.

d) Several hormones can influence a single aspect of growth and development.

e) Responses elicited by plant hormones probably result from changing ratios of hormones rather than from the presence or absence of any one hormone .

AUXIN stimulates cellular elongation, differentiation of vascular tissue, fruit development, formation of adventitious roots and the production of Ethylene. The most active naturally occurring auxin is Indoleacetic Acid (IAA). Synthetic auxins are used extensively in modern agriculture.

GIBBERELLINS stimulate extensive growth of intact plants, the transition from juvenile to adult growth, fruit formation and germination of some cereal grains.

CYTOKININS stimulate cellular division, expansion of cotyledons and growth of lateral buds. Cytokinins also delay senescence( a collective term for the processes contributing to the age-induced decline and ultimate death of a plant or plant part) of detached leaves and, in combination with IAA, may influence formation of roots and shoots.

ETHYLENE is a gaseous hormone that influences fruit ripening, abscission( the shedding of leaves or fruit by a plant ), sex expression and the radial expansion of cells.

ABSCISIC ACID ( ABA ) is an inhibitor that causes stomata to close, affects dormancy of some seeds and, in general, counteracts the stimulatory effects of other hormones.

Many botanists think that plant hormones are necessary for, but do not control, plant growth and development. According to this perspective, a plant's response to a hormone is not determined by the amount of hormone present, but rather by the sensitivity of the tissue to the hormone.

Last Updated on Monday, 05 December 2011 16:32
 
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