Snowdrops An Introduction


INTRODUCTION

ORIGIN AND CLASSIFCATION

Robert Dodoens first described snowdrops as a separate species in 1583. Even though the species was called Leucoion bulbosum triphyllon, the associated picture clearly illustrates a snowdrop (Stern, 1956). The species was described as a stranger to Belgium but as common in Italy.  In the sixteenth century pictures of snowdrops appeared and the term snowdrop originated from the word Scheetropfen, i.e. pendants worn in the sixteenth century. There are many folk names for these plants, some of which, such as ‘Fair maids of February’ and ‘Perce neige,’ reflect their time of flowering. Linneaus described the genus Galanthus in Systema Naturae in 1735.

Galanthus nivalis was first recorded wild in Worcestershire and Gloucestershire in 1770 (Bourne, 2000).

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The name Galanthus translates from Greek and means milk flower resembling snow. The genus contains eighteen species spread across Europe and Asia; most are woodland species though there are some grassland or mountain species. Galanthus Elwesii is named after Henry Elwes from Gloucestershire who introduced the species to Britain in 1874 from Mount Balansa in Smyrna Turkey where it had been discovered in 1854.

Snowdrops are classified by the vegetative characteristics of their leaves and their position relative to one another.  There are three groups:

  • The Nivalis group whose leaves are flat and applied against each other, e.g. nivalis The Plicati group whose leaves show externally recurved edges, e.g. G. plicatus
  • The Latifoli group whose leaves are rolled within each other at emergence, e.g. Elwesii (Le Nard & De Hertogh 1993).
 diagram

 Arrangement of leaves in groups of Galanthus species from left to right Nivalis group, Plicati group and Latifoli group

Within these groups the species have been separated by such characteristics as the markings on the inner segments, by the length of the pedicel in relation to the length of the spathe and by the colour and shape of the leaves. All of these characteristics appear to be reliable in classifying wild plants (Stern, 1956)

 sdrop flower

           

 galanthus elwesii

 

  1. Elwesii G. nivalis

BOTANY

Galanthus belongs to the subclass Monocotyledonae and the family Amaryllidacae and the basic chromosome number is n = 12 (Rees, 1992). All wild species are diploid with the exception of some forms of G. Elwesii subspecies elwesii which are tetraploid and G. rizehensis which has a triploid form. The tetraploid G. Elwesii exhibits considerable variability in the size of the leaves and the flowers, which could be as a result of its polyploid form (Stern, 1956).

Bulb structure

snowdrop bulb structure

The snowdrop bulb resembles that of the Narcissus but is much smaller and simpler. The storage organ is a truncated bulb, comprised of a tunic and two fleshy scales, which are the bases of the sheathing leaves and the bases of the two foliar leaves.

Each scale acts as a storage organ for a year.  A new bulb unit forms in the axil of the outer leaf and comprises a sheathing leaf, two foliar leaves and an apical flowering stem. Each scale is thickened on one half of the circumference by corrugations on the inner side beneath the epidermis and this thickening occurs on opposite sides of the two bulb scales. At flowering time airspaces are formed between each pair of the corrugations. In some bulbs, a second flowering stem is initiated at the base of the second leaf. Bulbs have a cold requirement that must be satisfied before the bulb can re-grow. Bulbs rest from the time the foliage dies down until early autumn. Immediately after the foliage has died down, accumulated assimilates are stored within the bulb, such that the bulbs have maximum size and possibly enhanced vigour at this stage. Flowers are initiated before the foliage dies down and cold is necessary for extension growth, with the timing of emergence and anthesis in spring determined by ambient temperature (Rees, 1992). Plant growth occurs in autumn and flowering can start in October for some species, however most species flower from January to March.

Leaves

Leaves are enclosed in a tubular membranous strongly ribbed sheath comparable with that of Narcissus. The species of Galanthus have been classified by the way in which the leaves appear out of the ground. The leaves may be narrow, broad or elliptic and in the Plicati group the margins of the leaves are folded outwards.

The colour of the leaves varies from deep green to glaucous green with a dull or polished surface.

Flower development

Flower initiation takes place immediately after flowering during late winter and by June the differentiation of the flower is complete. Flower initiation is only observed in bulbs of more than 4cm circumference. The scape is cylindrical or compressed, green or glaucous arising from between the leaves; occasionally more than one scape is produced from one pair of leaves. At the end of the scape, the spathe is formed of two green leafy bracteoles (Stern, 1956). These are joined at the margin by two membranes. One membrane splits to enable the flower and pedicel to emerge, the other shrinks in width drawing the bracteoles together, so that the membrane is hardly visible. In most species there is a white membranous margin at the point where the pedicel issues from the scape, though in some species of G. ikariae, G. fosteri and G. rizehensis this membrane is absent. The following stages have been observed during flower differentiation.

Stage 1.            Full initiation of the sheathing leaf and foliage leaves; the apex is still vegetative.

Stage 2.            Raising and broadening of the growing point and formation of the main growing point in the axil of the first foliage leaf.

Stage SP.         Both spathe leaves are initiated.

Stage P1.         The three tepals of the first whorl are fully initiated

Stage P2.         The three tepals of the second whorl are fully initiated.

Stage A1.         The three stamens of the first whorl are fully initiated.

Stage A2.         The three stamens of the second whorl are fully initiated.

Stage G.           Formation and development of the carpels.

Stage G+          Formation of the style.

Flower structure

The flower is pendant, and its position is reversed when it bursts as a bud from between the two spathes that form a protecting cover when it is first pushed above the ground. In all snowdrops, the flowers are solitary, white, globular or bell shaped and pendulous. The three inner segments of the perianth are considerably smaller than the three outer segments forming a kind of inverted cup around the stigma and stamens (Synge, 1961). The inner petals are notched at the tips and fused at the base and show a green mark around the tip

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Inflorescence of G. Elwesii                            Seed pod of G. Elwesii

Though generally single flowered, a double flowered form of G nivalis exists known as “Flore Pleno”.

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 The scape is in a central position between the leaves and has a length of between 10 and 20 cm (Le Nard & De Hertogh, 1993).

The anthers  of snowdrops do not dehisce to discharge pollen but are formed like sacks with a small opening at the mouth. If touched by an insect, pollen is scattered through the opening. The pollen may also be carried by the wind. Most of the flowers are fertilised by bees, which cling to the inner segments and insert their head and thorax in search of nectar and are coated with pollen in the process.  The style is longer than the stamens, white, slender with capitate stigma arising from the ovary, which is globose, green or glaucous composed of three loculi

Seeds

Galanthus is propagated by seed under natural conditions. The seed is light brown approx. 3.5 mm long and obtusely oblong with a fleshy caruncle, which is a light colour when fresh (Stern, 1956). Many species produce seed and the resultant seedlings flower in 3-4 years (Wilderspin, 1999). Snowdrop seeds germinate viviparously (Rees, 1992). Seeds can be sown as soon as they are ripe in summer.  Like some other bulb plants they have limited viability and therefore it is advisable to plant them when fresh (Rees, 1992).  The seeds will start to grow in the following spring and it takes between four to five growing seasons before flowering is observed; however, bulbets to be used as planting stock can be obtained after the second growing season (Le Nard & De Hertogh, 1993). Division of clumps of snowdrops before the foliage dies increases the numbers of bulbs the following spring.

GEOGRAPHICAL DISTRIBUTION OF GALANTHUS

The genus is confined to Europe, Asia Minor and the Caucasus. Galanthus nivalis has the widest distribution of all, being found throughout Europe from Spain in the West to the river Don in Russia in the East and as far north as Scandinavia. Stern (1956) reports that this species is not indigenous to Britain but has become naturalised throughout the country. Many subspecies are found in small geographical areas in Lebanon, Sicily and the Balkans. Several of these species flower in the autumn and have slightly different characteristics by which they may be identified. On the Greek islands, G. ikariae subspecies iIkariae is found.

G. ikariae

Galanthus Ikariae

Galanthus ikariae latifolius is indigenous to the Caucasus region.

Galanthus Elwesii elwesii is reported on the islands of Samoe and Thasos. This plant is prolific around Smyrna and H.J. Elwes is said to have received it from near Sofia (Stern, 1956). Galanthus Elwesii var. maximus occurs in the Balkans and has characteristic twisted foliage whereas G. graceus is indigenous to Thrace and Bulgaria. Galanthus fosteri is found in the north central area of Asia Minor near Amasia however it has also been found further south in Lebanon.

Galanthus fosteri

Galanthus fosteri

Galanthus rizehensis, a species that has triploid forms, is found near Trebizondit.

Galanthus rizehensis

Galanthus rizehensis

It  has characteristics of both G. ikariae latifolius and G. nivalis and grows in the same area as G. ikariae latifolius and may be derived from that species (Stern, 1956).Galanthus alleni is found in the province of Gruzia in the central Caucasus whereas G. caucasus grows throughout the western and eastern districts of the Caucasus and spreads as far as Iran.

Galanthus alleni

 galanthus allenii

In the East Caucasus in the province of Talysh, a Russian botanist named the species G. transcaucasicus about which nothing appears to be known outside Russia. Galanthus bazantinus is found in the area around Bursa east of the Bosphorus and has characteristics intermediate between those of G. Elwesii (inner segment markings) and G. plicatus (reduplicate margins to the leaves).

Galanthus bazantinus

Galanthus bazantinus

Galanthus plicatus can be found in the Crimea, but is also found in the Dobruja area. Another species with reduplicate leaves, G. woronowii, is described by a Russian botanist. This species is endemic in the area around Sochi east of the Crimea on the Black Sea coast. Nine species are found in Asia Minor and the Caucasus.

Galanthus plicatus

galanthus plicatus

Galanthus woronowii

Galanthus woronowii

Most Galanthus species are collected from the wild in Turkey and France, however this is ecologically unsound. Dutch statistics show that 59 million snowdrop bulbs were exported world-wide from Holland in 1989 (Hanks, 1991). Le Nard and De Hertogh (1993) state that The Netherlands exported 48 million snowdrop bulbs in 1985-1986.  Improved propagation techniques could eliminate the need for the depletion of indigenous populations.  The creation of self-sustaining commercial populations could lead to increased sales and greater diversity of species and hybrids available.

CULTIVATION

All the species are hardy and most are easy to grow as they multiply into large clumps of bulbs. Some species thrive in open sunny positions, for example G. Elwesii (Bowles, 1918) and G. caucasicus (Stern, 1956), others thrive best in semi-shaded conditions, for example  G. nivalis and G. plicatus (Synge, 1961; Mothew, 1973).

Galanthus nivalis under trees

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Galanthus nivalis in grassland

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Snowdrops flourish on chalk and clay soils.  They require an adequate supply of moisture and organic matter and thrive best with a certain amount of shading, as the foliage is susceptible to scorching.  They are intolerant of animal manure, but may be fertilised with dried blood or bone meal (Synge, 1961; Mothew, 1973).  All snowdrops are best moved and divided while they are making growth or just after they have flowered.  They are collected from the wild in late March / early April when the leaves are still green.  The bulbs are very sensitive to desiccation.  The soil pH must be near 7 to ensure well tunicated bulbs.  The bulbs are planted in August / September at a depth of 5 – 10 cm.  Some species, such as G. graecus and G. byzantinus, seed freely and different species cross with each other in cultivation (Stern, 1956) providing opportunities to develop new forms. Snowdrops are relatively free from pests and diseases though there are reports of stem nematode Ditylenchus dipsaci appearing in snowdrops (Rees, 1992).

Ditylenchus dipsaci

Ditylenchus dipsaci

 Symptoms resemble those found in narcissus, i.e. leaves are short, distorted and pale with a few elongated lesions. Bulbs are soft and when cut open reveal characteristic brown rings. There is no curative treatment available.

Damage to bulbs from Dulylenchus dipsaci

Bulbs also can contain a variety of fungal contaminants such as Fusarium spp.

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OBJECTIVES

In order to reduce the numbers of bulbs being removed from the wild it is necessary to improve commercial propagation of Galanthus bulbs. The main objective of the project is to investigate the vegetative propagation of Galanthus using chipping and micropropagation to determine the optimum method of propagating large numbers of bulbs. In order to propagate Galanthus bulbs, it is first necessary to reduce the microbial contamination within the tissues.  An optimum treatment has to be established for the surface sterilisation of tissue explants from bulbs using surface sterilisation, hot water treatment of bulbs and antimicrobial chemicals (antibiotics/fungicides). Snowdrops have been propagated through the production of adventitious shoots and or somatic embryos from leaf tissue, floral scapes and ovaries of G. nivalis & G. Elwesii cultured in vitro (Girmen and Zimmer, 1988a, b & c) and this method of propagation is assessed. There are many papers published on the production of adventitious shoots and somatic embryos from Narcissus a closely related bulb genus (Hussey, 1980; Sage et al., 2000; Hosoki & Asahira, 1980).

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