3THE TULIP PLANT

TPreviously a huge family with many genera, Liliaceae has now been reducedto only sixteen genera as a result of DNA (deoxyribonucleic acid) studies.These studies indicate major evolutionary groups and help in the analysis ofrelationships between families and genera. Genera formerly in the Liliaceaehave now been placed in separate families, such as Alliaceae, Hyacinthaceae,and Colchicaceae.Tulipa is one of the genera that has remained in Liliaceaeand is closest to Erythronium, the dog’s tooth violets, and Amana (discussedin chapter 7).

Characteristics shared by the sixteen genera in Liliaceae include the for-mation of a bulb, corm, or rhizome; the usually leafy stems; and either a soli-tary flower, or a simple or branched inflorescence. The flowers are composedof six perianth segments (tepals), six stamens, and a superior ovary. A supe-rior ovary is one that is held above the point where the tepals join the stem,so it is found within the flower. An inferior ovary is held behind this point,appearing behind the flower, as in snowdrops (Galanthus) and Narcissus,both in the Amaryllidaceae.

Tulips grow from a bulb that has a distinct outer layer called a tunic. Theleaves are often few, two to four being typical, and they are quite fleshy. Theyare held alternately on the stem, often crowded towards the base but some-times more spaced apart. They decrease in size up the stem and clasp it ratherthan having a distinct petiole. The flower is held erect and is composed ofsix free tepals, meaning they are not joined to each other at any point. Thereare no nectaries. The stamens and ovary are shorter than the tepals and heldwithin the flower, the ovary developing into a globular or ellipsoid capsulewith three compartments, each one filled with several flat seeds.

To the casual observer, the most obvious differences between tulips aresize and flower colour. Plant breeders have worked on these characteristicsto produce the multitude of different varieties of garden tulip that you seein bulb catalogues and planted in colourful spring bedding schemes. Dwarf

21

and sturdy or tall and bold, these hybrid tulips have flowers in every colourexcept blue and true black. The tepals may be delicately fringed or deeplycut, rounded or pointed, sometimes forming elegant, waisted blooms withpetals drawn out into long, fine points, as in the lily-flowered hybrids. How-ever, tulips differ in many other respects and, to see the complete range ofvariation, you need to study the species; after all, it is from these that the gar-den hybrids have arisen.

Some tulips may have more than one flower to each stem, and in thesmallest species these flowers may barely reach 1 cm (0.4 in.) from top tobottom. The leaves can be broad and rounded or narrow and linear, matt orshiny, pale green, deep green, grey, blue-grey, or grey-green, and they mayhave undulate margins. Sometimes the leaves are marked with brownishstreaks and blotches.

22 the tulip plant

Tulipa montana (left) with a

solitary, bowl-shaped flower

and several linear-lanceolate

leaves. Tulipa turkestanica

(top right) branching flower

stem. Tulipa sprengeri

(bottom right) flower, show-

ing the elliptic outer tepals,

the wider inner tepals, and

the six stamens surrounding

the single ovary.

Look even closer and you can detect less obvious differences, such as thecolour of the pollen, the hairiness of the filaments that hold the pollen-pro-ducing anthers, the shape of the bulb, and the presence or absence of hairson the leaves, stem, and bulb tunic. These minute but significant charactersmay not concern most gardeners, but to those with a keen interest in tulipsthey are what makes this group of plants so fascinating. These characters alsomake tulips infuriating because the various classifications of the genus arebased on them, yet in many cases they are not constant. This situation canmake it very difficult to decide where a species belongs within a classifica-tion and even what is a species and what is merely a variety or subspecies.The classification of tulips is dealt with in chapter 5, while this chapter looksat the parts of the tulip plant to highlight the terms used and the charactersto watch out for.

The Bulb

A tulip plant replaces its bulb every year. All the food stored in the bulb isused to produce the leaves, stem, and flower. Before the plant dies down forthe summer, it has to grow a new bulb, to allow it to survive without wateruntil the following winter.

The bulb is made up of a few thick, creamy white, fleshy scales. At thecentre of the bulb are the buds that will develop into the new leaves andflower. The largest bulbs can be 5 cm (2 in.) across, while the smallest maybe less than 1 cm (0.4 in.) across. The size of the bulb also depends on theage and health of the plant, reflected in its capacity to produce stored foodin the new bulb during the growing season.

On the underside of the bulb is the basal plate, with a semi-circular orarc-shaped zone from which the roots emerge. The bottom of the bulb isrounded but narrows towards the top, ending in a point. The outer layer ofthe bulb (the bulb tunic) can sometimes extend quite a distance beyond thebulb itself, forming a long, sharp point.

The features of the bulb tunic are important for distinguishing tulipspecies. This outer layer can be thick, tough, and leathery or thin, brittle,and papery. The colour is usually a shade of brown, sometimes almost black,and in some species it has a strong reddish tint. Carefully peel away the tu-nic and on its inner surface, in almost all the species, you will see some hairs.The function of these hairs is uncertain, but they could provide added pro-tection from the heat of summer or the cold in winter.

the tulip plant 23

It is common for hairs to be present at the top of the tunic and in a ringaround the basal plate.Tulipa montana,T. clusiana, andT. linifolia have sucha thick layer of hairs at the top of the bulb that they protrude in a promi-nent tuft beyond the tunic.

In several species, includingTulipa fosteriana andT. eichleri, the hairs arestraight and form an even layer over the inside surface of the tunic. Somespecies, such as T. subpraestans, have a hairless tunic but in others the hairscan be surprisingly dense and interwoven, forming a thick felt between thetunic and the bulb scales. This latter characteristic is a feature of the speciesclassified in sectionTulipanum, includingT. julia andT. agenensis.

In the wild it can sometimes be impossible to distinguish between twospecies without looking at the hairiness of the bulb tunics. Of course, to seethis feature requires digging up the bulb, something you really should not

24 the tulip plant

Tulip bulbs: (top row) Tulipa

sylvestris, T. hageri, T. humilis;

(second row) T. clusiana, T.

montana, T. kolpakowskiana,

T. turkestanica; (third row)

T. greigii, T. vvedenskyi ‘Tan-

gerine Beauty’, T. fosteriana;

(bottom row) T. kaufmanniana

‘Ancilla’, T. grengiolensis

do. With cultivated plants you can wait until they are dormant and if yougrow them in pots you can look at them when repotting.

As well as producing a new bulb every year, tulips often produce addi-tional bulbs (offsets) of varying size. It is not unusual to find three or fourbulbs in the place where last year there was one. A few of the offsets may beflowering size, the others can be grown on separately. In this way the tulipincreases itself vegetatively and all the offsets will produce new plants identi-cal to the original plant. Many species are stoloniferous, and the buds on thebasal plate that form the offsets grow outwards, forming a hollow tube witha new bulb at the end. Not only does the tulip increase in this way, but itspreads as well, creating an expanding colony.

A dropper is formed when a bud on the basal plate grows downwards,producing a new bulb at a much greater depth, occasionally up to 60 cm (2ft.) below the first bulb. This new bulb can completely replace the originaland in this way the tulip can delve deeper into the ground. This process ischaracteristic of seedlings which in the wild need to pull themselves downinto the ground to protect themselves from the heat of summer. Maturetulips prefer to be planted deep, but if they are too near the surface they toocan attain their desired depth by producing droppers. Some species, such asTulipa tarda, are very proficient at this.

The Leaves and Stem

You do not have to study tulips for long to realize how much the leaves varyfrom species to species. They emerge from the ground, the lowest leafwrapped around the second. It may be some time before the two leaves partto reveal any further leaves and the flower bud. Bulbs that are not going toflower will only produce one leaf.

The leaves are often glaucous (blue-grey to grey-green), but in Tulipasaxatilis andT. bakeri, for example, they are shiny mid-green and inT. tardathey are dull green. A few species have dark markings on the leaves, form-ing stripes or dashes. These marks are caused by the pigment anthocyanin,which also gives red-flowered tulips their colour. The most commonlygrown tulip with these markings is T. greigii. There is sometimes a line ofshort hairs along the leaf margin (ciliate). In some species likeT. lanata andT. ingens the whole leaf is covered in short, fine hairs (pubescent), whileothers have glabrous (hairless) leaves.

In the species descriptions I have given the dimensions of the lowest leaf,

the tulip plant 25

more freely given, the leaves become ‘softer’ and lose this character, espe-cially as they age.

The leaves are held on the stem, which grows from the bulb and termi-nates in either a solitary flower or branches to hold several flowers. Theflower stem begins where the upper leaf joins, which in multi-floweredplants is where the stem may branch. Alternatively the branches can arisefurther up, as inTulipa turkestanica.

The stem is either glabrous or pubescent and may be the same colour asthe leaves or stained with a darker colour such as red or purple, especiallynear the flower. In the wild, where bulbs are often deep down, a large por-tion of the stem will be underground. The stem lengths in the species de-scriptions refer to the aboveground portion, which is very variable and canbe different in cultivated and wild plants of the same species. In cultivation,light levels are often lower during the growing season than in the wild and

as this is almost invariably thelargest. The remaining leaves of-ten decrease rapidly in size upthe stem, but in some tulips theyare roughly the same size. Thedimensions vary enormously,from less than 1 cm (0.4 in.)wide, as in some forms of Tulipalinifolia and T. clusiana, to 16cm (7 in.) wide in T. fosteriana.Leaves can reach over 30 cm (1ft.) long but in most species theyare between 10 and 25 cm (4–10 in.). The lowest leaf is joinedto the stem at or just belowground level. The remainingleaves may be held close to thefirst like a rosette, as inT. tarda,or they are spaced along thestem, as inT. montana.

Tulip leaves come in variousshapes but are always longer

than they are wide. The following terms are commonly used to describetheir shapes:

Linear leaves are narrow with virtually parallel sides for most of theirlength.

Lanceolate leaves are usually wider than linear leaves and have sidesgradually coming together to form a point. They are widest nearthe base.

Elliptic leaves narrow at both ends and are widest at the middle.Ovate leaves are roughly egg-shaped with a pointed tip and are widest

near the base.Obovate and oblanceolate leaves are the reverse of ovate and lanceolate

so the widest point is near the tip.Oblong leaves are rectangular but with rounded ends.

One feature that is often lost in cultivation is the undulate (wavy) leafmargin, especially in tulips that grow in harsh environments, such asTulipasystola. Once in cultivation, where the sun may be less intense and water is

26 the tulip plant the tulip plant 27

05-11-F05 Tulips G4i_09_XServer04

Tulipa greigii ‘Red Riding Hood’ leaves

Tulipa systola in cultivation,

with longer stems than it nor-

mally has in the wild. The

large black blotch, narrowly

margined with yellow, can be

clearly seen at the base of

the bright red flower.

more freely given, the leaves become ‘softer’ and lose this character, espe-cially as they age.

The leaves are held on the stem, which grows from the bulb and termi-nates in either a solitary flower or branches to hold several flowers. Theflower stem begins where the upper leaf joins, which in multi-floweredplants is where the stem may branch. Alternatively the branches can arisefurther up, as inTulipa turkestanica.

The stem is either glabrous or pubescent and may be the same colour asthe leaves or stained with a darker colour such as red or purple, especiallynear the flower. In the wild, where bulbs are often deep down, a large por-tion of the stem will be underground. The stem lengths in the species de-scriptions refer to the aboveground portion, which is very variable and canbe different in cultivated and wild plants of the same species. In cultivation,light levels are often lower during the growing season than in the wild and

as this is almost invariably thelargest. The remaining leaves of-ten decrease rapidly in size upthe stem, but in some tulips theyare roughly the same size. Thedimensions vary enormously,from less than 1 cm (0.4 in.)wide, as in some forms of Tulipalinifolia and T. clusiana, to 16cm (7 in.) wide in T. fosteriana.Leaves can reach over 30 cm (1ft.) long but in most species theyare between 10 and 25 cm (4–10 in.). The lowest leaf is joinedto the stem at or just belowground level. The remainingleaves may be held close to thefirst like a rosette, as inT. tarda,or they are spaced along thestem, as inT. montana.

Tulip leaves come in variousshapes but are always longer

than they are wide. The following terms are commonly used to describetheir shapes:

Linear leaves are narrow with virtually parallel sides for most of theirlength.

Lanceolate leaves are usually wider than linear leaves and have sidesgradually coming together to form a point. They are widest nearthe base.

Elliptic leaves narrow at both ends and are widest at the middle.Ovate leaves are roughly egg-shaped with a pointed tip and are widest

near the base.Obovate and oblanceolate leaves are the reverse of ovate and lanceolate

so the widest point is near the tip.Oblong leaves are rectangular but with rounded ends.

One feature that is often lost in cultivation is the undulate (wavy) leafmargin, especially in tulips that grow in harsh environments, such asTulipasystola. Once in cultivation, where the sun may be less intense and water is

26 the tulip plant the tulip plant 27

05-11-F05 Tulips G4i_09_XServer04

Tulipa greigii ‘Red Riding Hood’ leaves

Tulipa systola in cultivation,

with longer stems than it nor-

mally has in the wild. The

large black blotch, narrowly

margined with yellow, can be

clearly seen at the base of

the bright red flower.

TulipPages_02 10/25/05 12:00 AM Page 26

can cause the stems to elongate as the flowers reach for the light. The lengthof the stem also varies as the flower ages. By the time the seed pods have de-veloped, the stem can be twice as long as when the flower first opened. How-ever, the length of the stem at flowering time gives you an idea of the size ofthe plant.

The Flower

In common with many other bulbous plants, tulips do not have separatesepals and petals. Instead, they have six colourful, similar-looking perianthsegments (tepals). The outer tepals act like sepals, surrounding the flower inbud. As the flower opens, the inner tepals are revealed, along with the sixstamens and the single ovary at the centre.

The outer tepals are often narrower than the inner three and their backsare frequently stained a different colour than the rest of the flower. In the

white-floweredTulipa biflora, forexample, the backs of the outertepals are greyish green. In somespecies, such asT. clusiana andT.kaufmanniana, the otherwisewhite or yellow outer tepals havered or purple colouring on theirbacks. The red-flowered tulipsare usually paler on the outsideor have a buff or pink blush.

Many of the terms used todescribe leaf shapes are also usedto describe tepals. They can beovate, lanceolate, obovate, or el-liptic, for example. They canalso be rhomboidal (diamond-shaped) or spathulate (spoon-shaped), where the tip isrounded and the tepal then nar-rows towards the base. Thewhole flower can be bowl-shaped, with a rounded base, orfunnel-shaped, with a narrow

28 the tulip plant

This yellow form of the otherwise red-flowered

Tulipa armena, from northern Turkey, has been

named T. galatica. This example has retained its

undulate leaf margins in cultivation.

base and opening wide to form a star. Funnel-shaped flowers are normallyconstricted just above the point where they join the stem.

Flower colour in tulips is immensely variable. For example, both red andwhite species have yellow forms. Pink tulips can range from almost white tolilac and purple. Red tulips can be orange-red, brownish red, scarlet, darkcrimson, or blood-red.

In the majority of species, the base of the flower inside is a differentcolour than the rest of the flower. This area is known as the basal blotch andit varies in size, shape, and colour. It is often a shade of black, blue-black,dark brown, or olive. It can be margined with white or yellow and this mar-gin varies in width. Some species have a yellow blotch at the base of a whiteflower, such asTulipa biflora,T. tarda, andT. turkestanica.Tulipa vvedenskyiis one of the red-flowered species with a yellow blotch, andT. saxatilis andT.bakeri are both pink with a yellow blotch margined with white. The diver-sity of flower colours and colour combinations is one of the reasons tulipsare so interesting to grow, but because colour is so variable, it is not a reli-able character to use when classifying the species.

One characteristic used to differentiate species is the presence or absenceof hairs on the filaments of theflower. The filaments hold thepollen-producing anthers andthese two structures make up thestamens, the male reproductivepart of the flower. Half thespecies of genusTulipa have glab-rous filaments. The other specieshave hairs on the filaments.These short hairs are usually in atuft or boss at the base but insome species, such as T. turkes-tanica and T. bifloriformis, thereare also wispy hairs along thewhole length of the filament.Hairy filaments are usually asso-ciated with fine hairs at the baseof at least the inner tepals.

The stamens surround theovary, which is usually a shade ofgreen, yellow, or creamy white

the tulip plant 29

Tulipa vvedenskyi flower

but can have darker staining towards the tip. At the top of the ovary is thestigma, which receives the pollen. The stigma is three-lobed and in mosttulips is sessile, meaning it is held directly on top of the ovary. In a fewspecies, including Tulipa uniflora, a style holds the stigma above the ovaryand can be up to 6 mm (0.25 in.) long. Once pollination has taken place,the ovary swells up and becomes darker. It eventually turns brown and brit-tle, before splitting open to release the flat, brown seeds stacked in threecompartments.

By studying the flower closely you can begin to identify a tulip or at leastthe group to which it belongs. Looking at the filaments you can immedi-ately assign the plant to one or other side of the genus. Also, hairy filamentsare usually found in funnel-shaped flowers and glabrous filaments in bowl-shaped flowers.

The flower colour, blotch size and colour, and the presence of marks orstaining on the outer tepals can also be helpful in identifying species, but re-member these characters can vary within a single population. The colour,shape, length, and number of leaves are also worth noting and, looking evencloser, the hairiness of the leaves and stems, the colour of the anthers and fil-aments, and in some cases the colour of the stigma. Do not forget to look at

30 the tulip plant

The flower of Tulipa turkestanica has wispy hairs along the length of its filaments.

the bulb if you can, especially the hairs on the tunic. Even if you are still con-fused, and there is no shame in admitting that you are, at least you are get-ting to know the plants more intimately. Only then will you really begin tounderstand them.

In the species descriptions, the months of the year indicating floweringtimes refer to plants growing in the Northern Hemisphere. The names ofthe seasons are, of course, interchangeable.

Genetics

To make sense of a genus in which the species are so morphologically vari-able, it can be useful to look beneath the surface, to study the geneticmakeup of the plants. The chromosomes of tulips have been studied sincethe early twentieth century and more recently, since the 1980s, the study ofDNA (deoxyribonucleic acid) has been used to work out relationships be-tween genera and the place of species within those genera.

Chromosomes are found within the nucleus of a cell and carry the ge-netic information, mostly in the form of DNA. The DNA carries the ge-netic code and so determines the exact makeup of an organism. Prior to acell dividing, the chromosomes become visible under a light microscope andcan be counted, giving the chromosome number. Tulips have a chromosomenumber of 24 (2n = 24). This is the diploid number. In normal cell division(mitosis) the resulting cells will have the same number as the original, butwhen a cell divides to produce gametes for sexual reproduction (meiosis),each new cell has half this number (haploid) so the nuclei of tulip pollengrains will have 12 chromosomes (n = 12). When the nuclei of two gametesfuse (from the pollen and egg cells), the resulting cell (the proembryo) willhave the normal complement for that plant.

It was soon discovered that many tulips have more than the basic num-ber of 2n = 24. This situation is not uncommon in plants and is called poly-ploidy. Tulips may be triploid (2n = 36), tetraploid (2n = 48), or pentaploid(2n = 60). These polyploid plants are usually larger and more vigorous, andthey often have reduced fertility so do not produce much viable seed. Theplants compensate by being more stoloniferous, allowing them to spreadvegetatively, but all the individuals will be exactly the same genetically.

A polyploid tulip arises from a diploid tulip so you could call it a second-ary stage in the evolution of a species. The reduction of fertility suggests thatpolyploidy is an evolutionary dead-end. It is from the fertile diploid plants

the tulip plant 31

that new species will eventually evolve. Sexual reproduction involves thegenes of two plants coming together to create a new individual. This iswhere variation among plants is initiated. The significance placed on poly-ploidy in the naming of tulip species varies from author to author, but with-out doubt the study of chromosome numbers has helped in the classifica-tion of the genus and in the understanding of its natural distribution.

The study of plant DNA (known as genetic fingerprinting) is more com-plex, but because it deals with the actual ‘building blocks’, the informationis more significant. Comparing the DNA of various closely related plantscan indicate how they have evolved and what their common ancestors mightbe. It can also show that two apparently similar plants have evolved inde-pendently of each other and are not closely related. This work is ongoing,notably at the Royal Botanic Gardens, Kew, but the conclusions so far, re-garding the genusTulipa, have been included in the classification in chapter5 and in the species descriptions in chapter 6.

One conclusion that can be drawn from DNA studies is that the smallgenus Amana is clearly separate fromTulipa. These species, which have pre-viously been included withinTulipa, are discussed in chapter 7.

32 the tulip plant