Inflorescence morphology of Lachiiaea and Cryptadenia ( Thymelaeaceae )

The current delimitation o f Lachnaea L. and Cryptadenia Meisn. is based on the inflorescence morphology. In Lachnaea both indeterminate and determinate inflorescences occur, whereas in Cryptadenia only determinate inflorescences are present. The indeterminate inflorescences in Lachnaea are capitate or umbellate. The determinate inflorescences in both genera comprise a solitary, terminal flower. It is concluded that the two genera cannot be distinguished on inflorescence structure.


INTRODUCTION
The Thymelaeaceae, which is regarded as a medium sized family comprising 50 genera and 720 species, occurs in both temperate and tropical regions (Mabberley 1990).Most genera belong to the subfamily Thymelaeoideae in cluding the genus Lachnaea L. and the genus Cryptadenia Meisn.Both these genera are endemic in the Cape Province.
In the classification systems of the Thymelaeaceae by Endlicher (1847, sec.Domke 1934), Meisner (1857).Bentham & Hooker (1880), Gilg (1894) and Domke (1934), Lachnaea and Cryptadenia have always been placed next to each other, reflecting their close affinity.Only one pre vious worker, Baillon (1880), did not regard Cryptadenia as a separate genus but as a section of Lachnaea.In the last taxonomic treatment of the two genera.Wright (1915) followed the classification of Bentham & Hooker (1880).
The floral morphology of Lachnaea and its closest re lated genus, Cryptadenia.is similar.The flowers are bisexual, tetranierous, apetalous, with eight floral scales inserted on the hypanthium below the insertion of the eight stamens, which are arranged in two whorls of four each.To distinguish between these two genera Wright (1915) used the inflorescence structure.In Lachnaea he regarded the flowers to be terminal, capitate or rarely solitary, whereas in Cryptadenia he described them as axillary, solitary and bibracteolate.A study of the descrip tions of the different taxa of both genera revealed that L axillaris Meisn., L micrantha Schltr.and L. ruscifolia Compton have flowers which are axillary and solitary, whereas the flowers of L penicillata Meisn.. according to Wright (1915), are terminal and solitary.If one should apply the criterion used by Wright (1915).the former three species should rather be placed in Cryptadenia.Thus, the criterion used by Wright does not hold.
A preliminary examination of herbarium specimens of the Western Cape herbaria has brought to light numerous misidentifications and incertae.illustrating the poor state of our know ledge of Lachnaea and Cryptadenia.The con fusion which presently exists regarding the delimitation of Lachnaea and Cryptadenia can be partly ascribed to the inconsistencies in Wright's interpretation of the in florescence morphology of these two genera (Wright 1915).As the inflorescence has been considered to be of great taxonomic importance in the past, the study of the inflorescence morphology was undertaken with the view to improving our understanding of these two genera.Meisner (1840) instituted three sections, Sphaeroclinium Meisn., Conoclinium Meisn.and Micmclinium Meisn., within Lachnaea.based on the inflorescence mor phology.In his later publication of 1857 he followed the same classification.In the section Sphaeroclinium he in cluded those taxa having a terminal, dense, manyflowered capitulum.which was either involucrate or evolucrate, the sessile flowers being arranged on a moderately thick, globose receptacle.Meisner (1840Meisner ( , 1857) ) included L. buxifolia Lam. and L ftlamentosa (Thunb.)Meisn. in this section.In the section Cono clinium he regarded the inflorescence as a terminal or sub terminal.few-to many-flowered, evolucrate capitulum.Here the moderately thick receptacle was at first hemis pherical to conical but by later elongating, became subcylindrical.From the regular arrangement of the flower scars on the receptacle, he regarded the inflorescence as a spike and not a capitulum.In this section he included L capitata (L.) Meisn.and L densiflora Meisn.In the section Micmclinium he included those taxa having flowers in sessile, terminal, subcapitate or subsolitary in florescences.or those rarely having axillary, solitary flowers, namely L. axillaris.L diosmoides Meisn., L ericoides Meisn.and L penicillata Meisn.Meisner (1840) regarded the flowers of Cryptadenia as terminal, solitary or geminate, or occasionally as axillary and solitary, but in his later publication of 1857 he described the flowers as being terminal and subsolitary.Gilg (1894) regarded the inflorescences in Lachnaea as usually being terminal, many-flowered heads, but oc casionally, when consisting of two flowers, as mostly axil lary.In Cryptadenia he regarded the flowers as solitary, axillary, with two bracteoles.Domke (1934) described the inflorescences in Lach naea as being usually terminal heads, which are basally enclosed by an involucre, or congested heads without an involucre.No mention was made of the solitary-flowered inflorescence in his generic description of the genus.In Cryptadenia he regarded the flowers as being solitary or few, either terminal or axillary with two bracteoles.Dyer (1975) followed Wright (1915) and also used the inflorescence structure to distinguish between Lachnaea and Cryptadenia.According to Dyer (1975) the flowers in Lachnaea are arranged either in terminal, bracteate or ebracteate heads or a congested spike, or are rarely solitary, whereas in Cryptadenia the flowers are axillary and solitary.
In the most recent publication on the inflorescence morphology of the Thymelaeaceae, Weberling & Herkommer (1989) regarded the inflorescences in Lachnaea as being capitate or spicate, or having solitary, axillary flowers borne on a proliferating spike as in L axillaris.In Cryptadenia they considered the flowers as being solitary and terminal.
From the above literature surv ey there seems to be con sensus with regard to the terminal, many-flowered heads but not with regard to the position of the single-flowered inflorescences in Lachnaea.Similarly in Cryptadenia dif ferent views are expressed with regard to the position of the inflorescence and the number of flowers in an inflores cence.
The aim of the present investigation was to determine whether the inflorescence morphology could be used to delimit the two genera.

MATERIALS AND METHODS
Material used in this study comprised herbarium specimens and plants collected in the wild, with the ex ception of L. nerxosa Meisn. of which fresh material was unobtainable.Eighteen taxa were selected.14 from Lach naea and four from Cryptadenia.The aim in selecting the taxa was to have as broad a representation as possible of all the taxa in the two genera.The criteria used for select ing the taxa were: 1, taxa representative of the three sec tions instituted by Meisner (1840), taking in account the variation in each section; and 2, taxa with solitary flowers.

Inflorescence structure within Lachnaea
Both major types of inflorescences, as recognized by Radford et al. (1974) and Cronquist (1988), namely in determinate and determinate, occur in Lachnaea.

Indeterminate inflorescences
Within the indeterminate inflorescences the capitulum and the umbel are represented.

Species with capitula
L buxifolia, L. capitata, L densiflora and L filamen tosa have terminal, multi-flowered, ebracteate capitula.These capitula are borne singly at the ends of branches on sericeous peduncles, which vary in length from 3 -1 0 mm.The sessile flowers are arranged on a moderately thick, convex receptacle, which elongates during the flowering period, becoming narrowly conical or conical.Different stages of flower development are present within a capitulum.The fruiting stage may be present basally while buds are still developing distally.An accurate num ber of flowers in an inflorescence is therefore not easily determined.The number of mature flowers, at a given time, varies from ± 50 in L. buxifolia, 20-50 in L. filamen tosa., ± 12 in L densiflora and only 1-3 in L. capitata.
After flowering, vegetative growth is resumed by lateral branches developing in the axils of the upper leaves immediately beneath the capitulum.These will eventually terminate in new capitula in the following flowering period.However, some of these lateral sh<x)ts, as in L densiflora, may terminate in capitula within the same flowering period.Lateral branches may also develop from the axils of the leaves below the distal leaf on the main flowering branches.These branches will, in the following flowering period, be terminated by capitula (Figure 1).

Species with umbels
Two types of indeterminate umbels, namely bracteate umbels as in L eriocephala and ebracteate umbels as in L diosmoides, are recognized.The pedicels remain in the old inflorescences tor some time after the upper portion of the flowers and the fruits have been shed.The number of pedicels present indicates the number of flowers in each inflorescence.

Species with sessile bracteate umbels
Sessile, bracteate umbels occur in L. aurea, L eriocephala and L penicillata.In L. eriocephala (Figure 2) the inflorescence is comprised of about 40 shortly pedicellate flowers, which are surrounded by a bracteate involucrum consisting of four large bracts, in two whorls of two.These bracts follow on the stem after the linearelliptic to lanceolate leaves.Similarly in L aurea the ± 50-flowered umbel is surrounded by 8-10 bracts which are spirally arranged.From the axils of the foliage leaves immediately below the bracteate umbels, vegetative growth is resumed by lateral branches in both species.These lateral branches will eventually terminate in brac teate umbels in the following flowering period.Lateral branching is not only restricted to the axil of the distal leaf when the leaves are alternately arranged as in L aurea, or to the distal pair of leaves, when opposite as in L eriocephala, but may originate from the axils of the other upper foliage leaves.These lateral branches are also terminated by bracteate umbels in the following flowering period.In both cases the lateral branches may elongate considerably.
In L penicillata (Figure 3) the inflorescence is also a terminal bracteate umbel.The umbel, usually eightflowered, is surrounded by four bracts, in two whorls of two each.Only the distal portion of a single mature flower is visible at a time.Wright (1915) inadvertently regarded the flowers as being 'terminal, solitary, sessile'.The elon gated pedicels and buds enclosed by the bracts were ig nored by him.Lateral branching arises from the axils of either the first or second pair of foliage leaves immedi ately below the inflorescence.These lateral branches may elongate considerably or may be reduced to comprising only one or two pairs of foliage leaves before being ter- minated by an inflorescence.Up to three generations of flowering branches may develop in one flowering period.
Vegetative growth is resumed by lateral branches develop ing from the axils of the upper foliage leaves of the last flowering generation.

Species with sessile ebracteate umbels
In L diosmoides, L ericoides, L funicaulis and L ner vosa the flowers are borne in sessile, ebracteate umbels at the tips of the branches.No bracts surround the in florescence as new vegetative growth arises from the axils of the leaves immediately beneath the umbel (Figure 4).
The number of flowers per umbel varies among the dif ferent species and also within each species.In L dios moides and L funicaulis 6 -2 0 flowers are present, where as in L. nervosa the number varies from 4-14 and in L ericoides from 2-8.As a result of the different develop mental stages of the flowers present in each umbel, only a few mature flowers are present at a time.Lateral branch ing is resumed from the axil of the upper leaves below the inflorescences but is not restricted only to the most distal leaves immediately behind the inflorescence.In L ner\osa (Figure 4) short, lateral branches also arise in the axils of the leaves lower down on the main flowering branch, which in the same flowering period are terminated by inflorescences.Consequently the main flowering branch has the appearance of a racemose inflorescence.
Similarly in L diosmoides lateral vegetative shoots arising in the axils of the leaves immediately below the inflores cence, may be terminated by inflorescences in the same flowering period.Here they may overtop the umbel on the main flowering branch, forming a dense cluster of umbels, and at the same time reduced lateral shoots may develop lower down in the axils of the foliage leaves of the same main branch with a racemose appearance, as in L nervosa.
In L. ericoides (Figure 4) a first and second generation of flowering shoots may occur.These shoots, as in the previous taxa, develop from the axils of the leaves imme diately below the inflorescence.Below the most distal leaf on the main flowering shoot, further lateral shoots may develop which may terminate in inflorescences in the same flowering period or in the next flowering period.These flowering shoots are, unlike those in L diosmoides, restricted to the upper leaves on the main flowering branch.Vegetative shoots may also develop lower down on the main flowering branches of the previous flowering period which again will be terminated by inflorescences in the following flowering period.

A C
2 mm In Lfunicaulis a pair of bract-like foliage leaves occurs at the base of the umbels.These umbels appear bracteate and resemble those of L penicillata, but, unlike L penicil lata, lateral vegetative growth develops in the axils of the bract-like foliage leaves.These lateral vegetative shoots will terminate in ebracteate umbels in the following flowering period.Reduced lateral shoots also develop in the axils of the upper leaves, behind the bract-like foliage leaves on the main flowering branch, which may terminate in ebracteate umbels within the same flowering period, forming a cluster of inflorescences towards the end of the main flowering branch.
In L burchellii (Figure 5), contrary to the interpretation of Meisner (1840Meisner ( , 1857) ) and Wright (1925) who regarded the inflorescences to be bracteate, the inflorescences are terminal, sessile, ebracteate umbels.The umbels consist of up to ten flowers, with 1 or 2 mature flowers at a time.Vegetative growth is resumed from the axils of the leaves immediately below the umbels.On some specimens the inflorescences appear to be bracteate.These 'bracteate' umbels are in fact reduced lateral branches, each ter minated by an ebracteate umbel.The leaves on these branches differ in size and shape from the foliage leaves on the rest of the plant.In the axil of the most distal leaf on one of these reduced flowering branches, a welldeveloped bud of the new vegetative shoot was observed.
The lower two pairs of leaves on some of the elongated lateral flowering branches, resemble those modified foliage leaves of the reduced flowering branches.These leaves are often caducous.Vegetative growth is resumed by lateral branches developing from the axils of the upper leaves immediately below the umbel and may also originate from the leaf axils lower down on the main flowering branch.These lateral branches will terminate in umbels in the following flowering period.Flowering branches may develop at random on the main flowering branch, as in L. nervosa.These flowering branches arise from the axils of the leaves behind the most distal leaf pair during the same flowering period.The main flowering branch thus has the appearance of a racemose inflores cence.

Determinate inflorescences
Meisner (1840) described the flowers of L. axillaris as being axillary, opposite or scattered, always solitary', with two intra-axillary bracteoles.In his later publication (1857) he referred to the flowers as being subsolitary, axil lary or rarely terminal.Wright (1915) regarded the flowers as being axillary and solitary.According to Weberling & Herkommer (1989) the flowers of L. axillaris are solitary, axillary with two transverse bracteoles.
The flowers of L. axillaris were found to be solitary and terminal.A well-developed bud of the new; vegetative shoot occurs in the axil of one of the leaves of the pair of foliage leaves immediately below the flower (Figure 6 ).Lateral branches, each terminated by a solitary flower, develop at random on the main flowering branches within the same flowering period.These flowering branches arise from the axils of the foliage leaves below the leaf pair immediately behind the terminal flower.These lateral flowering branches vary in length and may even be reduced to having one pair of opposite leaves.Conse quently the main flowering branch may have the ap pearance of a racemose or spicate inflorescence (Figure 6).Previous authors inadvertently regarded these leaves immediately behind the solitary flower as transverse brac teoles.It was found that the new vegetative growth originates in the axils of these leaves and terminates in flowers in the following flowering period.This growth is not always visible on herbarium material as specimens are usually collected when they are in full flower.
The flowers of L ruscifolia were regarded by Compton (1953) as being 'solitary, axillary, sessile'.On studying fresh material in the fruiting stage, we 11-developed vegeta tive buds were found in the axils of the bracteoles (Figure 7).These bracteoles are in fact bracteose foliage leaves similar to those found on the short lateral flowering shoots in L. burchellii.In L. ruscifolia the flowers are therefore solitary and terminal on much reduced, lateral, flowering shoots which develop at random in the axils of the foliage leaves on the main flowering branches giving them a spi cate appearance (Figure 7).Occasionally the lateral flowering shoot may consist of an additional pair of foliage leaves between the bracteose leaves (prophylls) and the flower (Figure 7).No terminal flower was ob served on the main branches probably due to the abortion of the apical meristem.From the axil of the leaf behind the aborted meristem new vegetative growth may resume or a reduced flowering shoot may develop (Figure 7).Two scarious prophylls which resemble the bracteose leaves on the lateral flowering shoot, occur at the base of the developing lateral vegetative shoot (Figure 7).Thus, in both L. axillaris and L ruscifolia the inflores cences are determinate, consisting of solitary, terminal flowers.

Inflorescence structure within Cryptadenia
The inflorescences in Crytadenia are all cymose.In all the taxa well-developed buds of the new proliferating shoot develop in the axils of the upper leaf pair immedi ately behind the flower (Figure 8 ).These vegetative sh(X)ts usually terminate in flowers in the following flowering period, except in C. filicaulis and C. grand (flora where they may terminate in flowers in the same flowering period.Lateral branches may also arise at random from the axils of the leaves beneath the distal pair below the terminal flower on the main flowering branch.These branches vary in length and may even be reduced to only the terminal flower and a pair of foliage leaves as in C. filicaulis (Figure 8 ).Consequently the main flowering branch, as in L axillaris, has the appearance of a racemose or spicate inflorescence.Lateral branches, each terminat ing in a solitary flower in the following flowering period, may also develop from the axils of the leaves lower down on the main flowering branches (Figure 8).

DISCUSSION
In the genus Lachnaea the flowers are arranged in ter minal, indeterminate, capitate or umbellate inflorescences, or they are solitary and terminal.In Cryptadenia the flowers are solitary and terminal.Determinate inflorescen ces occur in both Lachnaea and Cryptadenia, whereas indeterminate inflorescences occur only in Lachnaea.Table 1.
In both genera the differentiation of a long shoot/short shoot system can be observed.In some taxa within Lach naea and Cryptadenia this system is more conspicuous than in others.In both genera new vegetative growth arises from the axils of the foliage leaves immediately below the inflorescences, and this may terminate in an inflorescence within the same flowering period.Thus two generations of flowering branches may occur together on a plant (Figures 4 & 8).Weberling & Herkommer (1989) regarded the terminal, single-flowered inflorescence found in Cryptadenia as a monotelic inflorescence.The inflorescence in L. axillaris and L ruscifolia can therefore be regarded as monotelic.The polytelic inflorescence on the other hand would, ac cording to their terminology, include the capitulum and umbel in Lachnaea.According to Weberling (1983) the polytelic type of inflorescence has probably been derived repeatedly from the monotelic type during the evolution of angiosperms by the reduction of the terminal flower and specialization of the paracladia of the monotelic sys tem.The distal elements are reduced to single lateral flowers or lateral cymes, which constitute elements of an apical system composed of lateral flowers.Therefore the floral axis, instead of terminating in a single flower, ter minates in a multi-flowered polytelic inflorescence.
According to Weberling & Herkommer (1989) Gonystylus Teijsm.& Binn.and Amyxa van Tiegh. of the Gonystyloideae which is regarded as a relatively primitive group, have monotelic synflorescences (synflorescence according to Weberling 1983).Within the Thymelaeoideae, the Gnidioideae and probably the Aquilarioideae, certain taxa were also found to have monotelic synflorescences.They came to the conclusion that, con sidering the other more or less primitive characters and the different taxonomic evaluation of those combinations, it was impossible to draw any taxonomic conclusions ex clusively from the existence of the monotelic synflores cences within those taxa.
FIGURE 2.-L eriocephala, Beyers 54. A. diagrammatic illustration of branching pattern of flowering branches; B. bracteate umbel with flowers and bracts removed; C. abaxial view of one of inner pair of bracts; D, abaxial view of one of outer pair of bracts; ■ remains of previous year's inflorescence; V, umbel; b, scar of removed bract; p, pedicel.
FIGURE 6.-L axillaris.A, flowering shoot illustrating new vegeta tive shoot in axil of distal leaf, Morley 174; B. diagrammatic illustration of branching pattern of flowering branches; ■ .scar of flower of previous year; ©, flower bud; O, open flower; # .fruit.
FIGURE 7.-L ruscifolia.A, branch illustrating aborted apical meristem (a) being displaced by new lateral shoot developing from axil o f distal foliage leaf.Marshall J9; B, main branch with short lateral flowering shoot, VIok 166; C, diagrammatic illustration of branching pattern of flowering branches; D, flower bud with two bracteose leaves (p), Vlok 166; E. vegetative shoot (v) arising from axil of one of bracteose leaves; f, flower; fl, foliage leaf; A. aborted apical meristem; ©, flower bud; O , open flower: • .fruit; ■ scar of flower o f a previous year.