ANATOMY, MORPHOLOGY, AND CLADISTIC ANALYSIS OF MONSONIA L. (GERANIACEAE)

ALDASORO, J.J.. C. NAVARRO, P. VARGAS & C. AEDO (2001). Anatomy, Morphology, and Cladistic Analysis of Monsonia L. (Geraniaceae). Anales Jard. Bot. Madrid 59(1): 75-100. Phylogenetip relationships among the 25 species of the old-world genus Monsonia are explored by means of a cladistic analysis. After a detailed revision, 20 morphological and anatomical characters were selected, including some new ones from nectaries, androecium, and mericarps. Phylogenetic analysis yielded 9 most parsimonious trees. The strict consensus tree showed two major clades: one is formed by the 9 species of Monsonia sect. Monsonia, characterised by plumose awns, plus Sarcocaulon; and a second with the 16 species of Monsonia sect. Olopetalum which share the type of mericarp detaching, consistency of columella and the thick mericarp walls. Consequently, some doubts about the monophyly of Monsonia exists. However, the current infrageneric classification of Monsonia is supported after transferring M. longipes and M. speciosa to sect. Olopetalum. Several characters of the mericarp are related to zoochory, which seems to be a derived syndrome in Monsonia, as in the other Geraniaceae.

ALBERS (1996) reconsidered the circumscription of Sarcocaulon and Monsonia, suggesting that there is no reason for maintaining both genera as separate.He based his decision on criteria such as similarity in flower structure, phenolic compounds, protein patterns and chromosome numbers.However, some of these data are still unpublished.DREYER & al. (1997) and MOFFET (1997) criticised Albers' proposal on the grounds that the present knowledge of the genus is not sufficient and a molecular study is needed.Besides, these authors consider that macro-morphological differences between the two genera are clear and well-defined.
Apart from the two comprehensive monographs (KNUTH 1912;VENTER 1979), partial studies of Monsonia were carried out on pollen morphology (VERHOEVEN & VENTER, 1986), embryology (NARAYANA & ARORA, 1963), mericarp and seed arrangement (YEO, 1990), anatomy of nectaries (LINK, 1990) and phytogeography (VENTER, 1983).A grouping analysis based on morphological features was performed by VENTER (1990), supporting his sectional treatment of Monsonia.KERS (1968) and VENTER (1983) assessed the geographical distribution and habitats in Monsonia.The 25 species inhabit grasslands, savannas, and deserts in Africa and Southwest Asia.The highest diversity of the genus can be found in southern Africa with 21 of the 25 species, of which 9 are endemic to South Africa and 7 to Namibia.
Previous studies in Monsonia show a remarkable broad range of morphological variation (VENTER 1979).Species vary in life form, root type, leaf and stipule shape, inflorescence types, sepal and gynoecium indumentum, petal size, nectary types, anther size, stamen number, exine ornamentation, stigma size and shape, fruit features, cotyledon arrangement.
A phylogenetic study of Geraniaceae using rbcL sequences was performed by PRICE & PALMER (1993).They found Sarcocaulon to be sister to Monsonia, with Pelargonium sister to the other four genera of Geraniaceae.The relationship between Monsonia and Sarcocaulon is also supported by the loss of the rpl2 intron (PRICE & al., 1990;DOWNIE & PALMER, 1992).
The specific objectives of this study on Monsonia were to: 1) re-evaluate morphological characters used in previous monographs; 2) search for new morphological and anatomical characters; and 3) analyse phylogenetic relationships among the species using parsimony.

MATERIAL AND METHODS
This paper is based on herbarium specimens, studied in the following herbaria: B, BM, COI, G, K, LE, MA, MO, MPU, P, W and WAG.Specimens used in anatomical studies are listed in Appendix 1.In this study we follow the taxonomic treatment proposed by VENTER (1979,1983).
Dried flowers from herbarium specimens were soaked in warm water with 1 % NaOH or with 2-3 drops of liquid soap; after two hours they were transferred to water for one hour and then to 50 % ethanol.Mericarps and flowers removed from herbarium specimens were rehydrated for light photography, hand-cut sections obtained, and tissues differentially stained.Sections were made with a SLEE-MAINZ-MTC microtome, stained with Fasga mixture, which is made of Safranin and Alcyan green 2GX (Gurr Chemical Co.) (To-LIVIA & TOLIVIA, 1987), and photographed by light microscopy.Flowers and mericarps were sectioned, glued on aluminium stubs,   4. Spines absent (0); spines present (1). 5. Leaf veins palmate or subpalmate (0); leaf veins pinnate or subpinnate (1).
19. Mericarp wall narrower than 20 mm (0); wider than 30 mm (1).20.Seed with plane cotyledons (0); moderately folded cotyledons, non conduplicate (1), clearly folded, conduplicate cotyledons (2).coated with 40-50 nm gold, and examined in a JEOL-TSM T330A scanning electron microscope (SEM) at 20 kV.Cladistic analyses species were conducted using Fitch parsimony (as implemented in PAUP 3.0; SWOFFORD, 1993) with unordered and equal weighting all characters.Heuristic searches were replicated 100 times using random taxon entries and ACCTRAN optimization.The 25 species belonging to the two sections of Monsonia (9 in sect.Monsonia and 16 in sect.Olopetalum) were included as the ingroup.Pelargonium peltatum, was chosen as the outgroup based on previous chloroplast sequence analyses (PRICE & PALMER 1993) in which this genus is basal to the other genera of Geraniaceae: Sarcocaulon, Erodium, Geranium, and Monsonia.Other species of Pelargonium were also studied in order to test if some states of a character were present in all of them.To test the monophyly of Monsonia, three species of Sarcocaulon (S. crassifolium, S. marlothii and S. mossamedense) were also included in the analysis.MacClade version 3.04 was used to reconstruct character evolution (MADDISON & MADDISON, 1992).Reliability of clades was assessed by bootstrapping (using 100 replicates addition) (FELSENSTEIN, 1985).A total of 20 morphological and anatomical characters (tables 2, 3) were used in the cladistic analysis, two of them being quantitative (anther length and mericarp wall width).Some other characters were studied but finally excluded from the analysis because of either high instance of polymorphism or we did not observe discontinuities to define character states.The excluded characters are: presence of tuberose roots, subacaule or acaule habit, presence and length of sepal mucro, petal size, presence or absence of stalked glandular hairs on the ovary, shape of bristle tip and pits on the mericarp body, reticulate ornamentation and papillae types on the mericarp surface, and presence and distribution of glandular hairs.

Morphological characters
A matrix of characters with potential phylogenetic information is shown in tables 2 and 3, and discussed below.
? 0 1 0 0 0 0 0 0 0 ?0 0 0 0 0 1 1 0 0 0 0 0 0 0 0 0 0 (perennials); and (3) horizontal, woody or stout rhizomes, often sheathed with old stipules on the base of plant, more or less branched, generally without tubers.Many of the species of Pelargonium have vertical branched roots, while others have tubers.Caulescence is the rule in Monsonia, but some species have a tendency to adopt a rosulate appearance, and the stagnation of growth makes them almost acaulous, such as M. deserticola, M. drudeana, M. heliotropioides, M. ignorata, and M. nivea.Sarcocaulon are fleshy shrublets covered with waxy bark (tables 2 and 3, characters 2 and 3), features which never occur in Monsonia.The bark is formed by a phellogen; which produces a wide phellem to the outside and several layers of phelloderm cells toward the inside (MOF-FETT, 1997).Also, some species of Pelargonium are succulent, but none has a bark impregnate of wax and resin (Moffett, 1997).P. peltatum has a herbaceous habit.
Spines, leaves, leaf shape and venation.-Species of Monsonia lack spines, while in Sarcocaulon the spines are formed from the long petioles after the laminas fall off (tables 2 and 3, character 4) (Moffett, 1997).Leaves are divided only in M. speciosa and M. longipes.Monsonia speciosa includes lobed, palmate, palmate-lobed, and palmatifid leaves (VENTER, 1979).Two main types of leaf venation can be recognised in Monsonia: subpalmate to palmate, and subpinnate to pinnate, (tables 2 and 3, character 5).Only two species have palmate veins: M. drudeana and M. ignorata, while in M. deserticola, M. heliotropioides, M. luederitziana, M. parvifolia, M. trilobata, and M. umbellata veins are mostly subpalmate.Pinnate or subpinnate veins are found in all other species of Monsonia.Palmate or almost palmate veins occur in most species of Pelargonium and Sarcocaulon.
Stipules.-Alarge range of variation of stipule shapes occurs in Monsonia.Twelve species have oval to lanceolate stipules whereas the remaining 13 species have linearlanceolate to subulate stipules.Pelargonium include both linear and lanceolate stipules (tables 2 and 3, character 6).Tuft hairs were found on the stipule apex of 15 species, whereas we did not find this character neither in the remaining 10 species nor in Pelargonium (tables 2 and 3, character 7).
Inflorescences.-Axillar flowering stems are found in all species, being also terminal in some of them.Development of terminal or axillar flowering stems is however not consistent within the same species.There are two significant inflorescence types: cymes and pseudoumbels.Thirteen species of Monsonia have cymes, while 10 species have pseudoumbels, as do most Pelargonium species (tables 2 and 3, character 8).Inflorescence of two Monsonia species bears only a single flower (M.drudeana and M. speciosa).Other than the 13 species with cymes, we have observed only monochasial inflorescences, except in M. burkeana and M. emarginata where they can be both, dichasial and monochasial.Also, all studied Sarcocaulon bear solitary flowers.
Sepals.-lmbric&te, persistent sepals are found in all species of Monsonia.Concave sepals retain nectar, being sometimes connate or somewhat enlarged (figs.If,3B and 3C).A group of five species have sepal enlargement at the base in such a way that an appendage encloses an axillar nectary (pouches).This pouch is limited laterally by walls that connect the sepals with the base of the staminal filaments (figs.4A, 4B and 4C) (tables 2 and 3, character 9).The cavity is covered by hairs (figs.4D and 4E) and has stomata on the epidermis (fig.4F).Five representatives of sect.Monsonia {M.umbellata, M. parvifolia, M. luederitziana and M. ignorata) show pouches.Pelargonium and Sarcocaulon lack pouches and sepal or staminal enlargements.

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Nectaries.-There are five episepal nectaries in Monsonia, placed on the base of each group of three joint staminal filaments.The nectaries have a secretory parenchyma with intercellular spaces inside and anomocytic stomata generally on its surface (figs 3F, 4F, 5C and 6E).They are vascularized by branches of phloematic sepal bundles.Usually, the branch that goes to sepal and stamen also reaches the nectary (figs 3E, 4B and 5E).From our anatomical studies we have coded nectaries as two main types considering the position of secretory tissue: (1) axillar nectaries, with secretory tissue at the sepal axile (fig.3A-E); and, (2) secretory knobs, with prominent tissue (knob) on the base of each group of three joint staminal filaments.The latter type includes two subtypes, one has the secretory tissue on the outer part of the knob and has no hollow inside (fig.5A-F), and the second has the secretory tissue on the inner part of a hollow located behind the knob, while the external part of knob has no stomata (fig.6A-F, tables 2 and 3, character 10).The size and shape of the knobs are variable between species.All the types of nectaries are often followed by a shallow channel along the group of filaments, with two rows of hairs which serve to lead the nectar upwards (fig. lc, lg, 2j, 4D and 4E).The disposition of hairs, the channel and the size of nectaries are variable.
Androecium.-Monsonia has 15 anthers gathered in groups of three filaments, the highest number in the family (VENTER, 1979;YEO, 1990).The stamens form a tube with 5 groups of filaments fused more or less along the length.Here we report for the first time an exception to this pattern in Monsonia for M. brevirostrata, which has only 5 fertile stamens plus 10 sterile filaments.Thus, each central anther of the group is fertile, while two lateral anthers abort (fig.2j).Anther size varies in Monsonia.There are seven species with small anthers (less than 1 mm) and the remaining eighteen have distinctly long anthers (tables 2 and 3, character 11).Anther size is usually related to pollen content.The pollen content per anther varies in Monsonia.VENTER (1986) reported a striklingly low number of pollen grains in M. nivea and M. heliotropioid.es(8-10 per anther), while in most other species it reaches more standard features (i.e.740-900 grains per anther in M. speciosa, counted in this study).
Pollen  7D).Presence of supratectal processes was coded for the cladistic analysis (tables 2 and 3, character 12).The Erodiumtype pollen has been found only once in M. deserticola and thus it was not considered in the cladistic analysis.Other details, not coded in the analysis, are the externally serrate tectum in M. speciosa and the slightly wavy and dense muri in M. drudeana, M. luederitziana, M. parvifolia, and M. umbellata.Pollen in Sarcocaulon is similar to type 1 in Monsonia, while in Pelargonium it is very variable, and in P. peltatum is also reticulate, but with smaller cells (STAFFORD & GIBBY, 1992).Most of these types of pollen in Monsonia have been reported by BORTENSCHLAGER (1967) and VERHOEVEN & VENTER (1986).
Gynoecium.-Ths,ovary is superior, terminally beaked, 5-lobed, and 5-locular.Each carpel contains 2 axilar, campylotropous ovules, the lower being abortive (NARAYANA & ARORA, 1963;BOESEWINKEL & BEEN, 1979;BOESEWINKEL, 1997).The style is obsolete, with 5 stigmata, linear or clavate, or rarely short and ovoid or rounded (fig.8A  and 8B).The ovary base has sometimes tubular hairs with basal glands, which produce a smelling secretion.Other species have verrucate (i.e.M. nivea) (fig.8D) or glandular hairs (i.e.M. senegalensis) (fig.8C and  8F) on the top of the ovary.The glandular hairs can suffer a transformation or perdure until fruit maturation (fig.8E).The tip of glandular hairs has special structures to secrete substances (fig.8C, 8F and 9 A)! Ovary ornamentation is either highly variable or typical ones are present in only a single species, which makes this character not useful for cladistic analyses.
Fruit.-lt is a rostrate schizocarp with 5 mericarps.The mericarps are tailed on the top, the awn being as long as the schizocarp beak.When the mericarp is ready to be dispersed the tail detaches from the central axis (columella) (YEO, 1984(YEO, ,1990)).We have coded this character into two states depending on awn detaching: (1) in Monsonia sect.Olopetalum, the upper part of the tail separates along the columella and then the mericarp body (fig.2e); (2) alternatively, in Monsonia sect.Monsonia the distal part of the awn remains attached to the columella while the mericarp body detachs (fig.Id) as in Sarcocaulon and Pelargonium (tables 2 and 3, character 13).After mericarp detachment, the awn becomes twisted and some hairs become visible on the internal surface to facilitate the mericarp dispersal by the wind or other means.The columella in sect.Olopetalum is short and stout while in sect.Monsonia is very long and weak (tables 2 and 3, character 14).Although one of the outgroups (Sarcocaulon) has long and weak columella, Pelargonium peltatum has a stout columella.This character needs a detailed study in Pelargonium.
Awn.-All representatives of Geraniaceae have hairs on the inner part of the awn.These hairs are similarly long on both the lower and upper parts in sect.Monsonia (plumose awns of Boissier's sect.Plumosae), whereas they are long on the lower part but short on the upper in sect.Olopetalum (not plumosae awns of Boissier's sect.Barbatae; table 1).Monsonia trilobata (sect.Monsonia) is an exception because it has not plumose awns (tables 2 and 3, character 15).Most species of Pelargonium are not plumose, while all studied Sarcocaulon are plumose.Awn fibres suffer changes in length when moist, causing mericarp rotation that helps to bury the mericarp (fig.9C and 9F; COBELLI, 1892).
There are two types of structures on the mericarp near the abscission point: ridges and pits (figs.9D, 9F-G, 10A-F and 10J).Pits are concavities situated symmetrically on both sides of the upper part of mericarp.that have glands or other secretory devices (figs.10A, 10F and 10J).Pits are formed by collapsing several layers of developed exocarp cells (fig.9F, G).The pit is obscure or absent in some species of Monsonia sect.Monsonia, such as in M. deserticola, M. heliotropioides, M. ignorata, and M. nivea (fig.9D and 101).One or two transverse ridges may or not be present on the upper part of the mericarp body (figs.9D, 10C-E).These characters were not used due to high variability observed in both pits and ridges in Monsonia.
Indumentum.-Mcricarp indumentum is formed by many types of hairs.A comprehensive classification of them was reported by Venter (1990) 12A-D, 12F-H), whereas the remaining species have short and long bristles on the mericarp (fig.11E-F) (tables 2 and 3, character 17).Similar, long bristles cover the meri- showing the cavity formed between the base of a stamens group <st) and the sepals; two walls (w) connect the stamen filaments with the sepals and close the cavity.The nectary is followed by a channel (ch) along the group of filaments, with two rows of hairs (h), which lead the nectar upwards.E: SEM micrograph of nectary of M.parvifolia showing this cavity covered with hairs.F: SEM micrograph of surface ofM.parvifolia nectary showing one stoma (s) and hairs (h) (Schlechter s.n., W).  carp body in all species of Pelargonium and Sarcocaulon.

Cladistic analysis
The cladistic analysis using Pelargonium and Sarcocaulon as outgroups, yielded 9 minimal length cladograms consisting of 37 steps, a consistency index (CI) of 0.621, a retention index (RI) of 0.913, a rescaled consis- tency index (RC) of 0.567, and a homoplasy index (HI) of 0.378.The strict consensus tree recovers two major clades (fig.14), one of these clades includes some of the outgroups (Sarcocaulon).The first major clade consists of all species of M. sect.Olopetalum and is defined by three synapomorphic characters from the mericarp: mode of detaching (character 13), wall width (character 17), and cotyledon folding (character 20).This clade is supported by 85 % bootstrap.Monsonia speciosa is sister to the rest of the species of M. sect.Olopetalum (88 % bootstrap) (subclade I), as a result of one synapomorphy (plane stipules, character 6).
The second major clade (76 % bootstrap) includes the species of sect.Monsonia and the three species of Sarcocaulon forming a politomy.The clade is defined by two synapomorphies: folded, but non-conduplicated cotyledons (character 20) and plumose awns (character 15).There is also a weakly supported subclade formed by M. deserticola-M.nivea-M.heliotropioides (subclade VI) supported by an non-synapomorphic change (anthers very small, shorter than 1 mm, character 11).The three species of Sarcocaulon form a clade (96 % bootstrap) defined by three synapomorphies: stems fleshy and covered with waxy bark (characters 2 and 3) and spines formed from petioles of long leaves (character 4).

Monophyly of Monsonia
Monophyly of Monsonia is challenged by the inclusion of Sarcocaulon in a clada togeth- er with Monsonia sect.Monsonia.Thus, AL-BERS ' (1996) criterion lhal Sarcocaulon should be included in Monsonia is supported by our analysis based on morphological characters.However, according to MOFFETT (1997) these changes could be premature and cause nomenclatural instability.At the present status of knowledge we prefer to maintain Sarcocaulon as a separate genus, until more independent evidence is available.

Cladistic Analysis and Classification of Monsonia
The results obtained from the cladistic analysis are in agreement with the division of Monsonia into two groups: M. sect.Olopetalum (= Barbata) and M. sect.Monsonia (-Plumosa)(Venter, I979)(table l).Two species (M.longipes and M. speciosa) were placed in sect.Monsonia by VENTER (1990) and VERHOEVEN & VENTER (1986) based on a cluster analysis of morphological characters.However, these two species share the three synapomorphies of M. sect.Olopetalum (mode of detaching, wall width, columella consistency, and cotyledon folding), and thus fail within the clade of this section, (tables 2 and 3).
In contrast, M. sect.Monsonia is only defined by two synapomorphies: folded, but non-conduplicated cotyledons and plumose awn.
In the analytic classification proposed by KNUTH (1912) (table 1) there are some natural groups; although we do not consider any taxonomic status for sect.Biflora, two species (M.brevirostrata, M. angustifolia) included in that section by Knuth form a natural group together with M. senegalensis in our analysis (subclade IV, fig.14).Otherwise, Knuth's sections were not supported in the cladogram: Umbellaiae, Ovata, Gentstiformis, and Roiundatae.
Sarcocaulon is monophyletic.The three synapomorphies supporting its clade are also shared by the species not included in this analysis: succulent stems (character 2), stems covered by wax (character 3), and spines formed from leaf petioles (character 4).

Character differentiation and evolution
Most characters analysed in this study were already discussed by VENTER (1979).We have revisited all of them and searched for additional taxonomic information.
The annual life span seems to have arisen only once in Monsonia.The three annual species (M.angustifolia, M. senegalensis, M. brevirostrata) are usually colonizers.Two of them are distributed in a wide range of distribution and altitude, whereas M. brevirostrata occurs on mountainous bare ground (VKNTER 1979).Although most annuals are derived in Geraniaccae (incl.Monsonia), there are several instances in Pelargonium (BAKKHR & al !998) and Geranium (YEO 1973) where perennials derived from annuals.
Leaf characters appear to have followed two different evolutionary patterns.Pinnate leaves have appeared twice, once involving most species of sect.Olopetalum and, independently, in M. nivea (sect.Monsonia).In contrast, subulate stipules and hair tufts occured once within sect.Olopetalum.
According to YEO (1990) pseudoumbels are considered an advanced feature in Geraniaceae due to suppression of bracts and internodes.Our cladistic analysis suggests that pseudoumbels in Monsonia are primitive while cymose inflorescences are derived.
Nectary features were already described in the literature (NARAYANA & ARORA, 1963; AL-NOWAIHI & KHALIFA, 1973;KUMAR, 1976;LINK, 1990;VOGI-X, 1998).It is commonly accepted that they are derived from hydathodes in Geraniaceae (LINK, 1990;VOGEL, 1998).LINK (1990) published a schematic and comprehensive classification of Geraniaceae nectaries, with three types: cryptothetic-staminal, phanerothctic-discoid, and cryptothetic-hypanthial.In Monsonia we have re-interpreted Link's classification considering three types: axillar, staminal with a protuberance, and staminal with a tube.In general, Link's cryptothetic-staminal are axillar and Link's phanerothetic-discoid are staminal with a protuberance.However, part of Link's cryptothetic-hypanthial nectaries are actually axillar, while the rest are staminal with a tube.A second character is found in a sepal structure related to nectar protection from desiccation: an enlargement at the sepal base, which encloses the nectary in pouches and is related to part of axillary nectaries.This structure was interpreted by Link as part of cryptothetic-hypanthial nectaries.Staminal nectaries with a protuberance have occurred twice, once involving some of species of sect.Olopetalum (subclades IV and V plus M. burkeana and M, praemorsa) and, independently, in part of sect.Monsonia (subclade VI).In contrast, staminal nectaries with a tube occurred only once within sect.Olopetalum.(subclade III).Additionally, sepals with pouches have appeared once within Monsonia, defining subclade vn.
The androecium in Monsonia consists of 15 anthers, except for M. brevirostrata which has a reduction to 5 fertile stamens plus 10 sterile filaments.Fertile stamen reduction has been observed in other genera of Geraniaceae such as in Pelargonium (VAN DER WALT, 1990), Geranium pusillum and G. biuncinatum (AEDO & al. 1998, and unpublished data).Reduction in anther length (< 1 mm) has occurred once within sect.Olopetalum (subclade IV) and twice in sect.Monsonia (M.deserticola, M. nivea plus M. heliotropioid.es; and M. umbellata), being likely associated with a shift to autogamy that has brought also a reduction in the number of pollen grains (as few as 8 in each anther of M. heliotropioides) and petal size (1.5 mm in M. nivea).
Supratectal processes define a clade of two species (M.nivea and M. heliotropioides) within sect.Monsonia.Similar processes are present in many species of Geranium and Erodium, whereas Sarcocaulon and Pelargonium lack this character.
Four of the seven fruit characters considered in the cladistic analysis define the two sections of Monsonia.Mericarp detaching, consistency of columella, and mericarp wall thickness support the monophyly of sect.
Olopetalum, while plumose awn characterises sect.Monsonia.The two types of mericarp detaching were first found by PICARD (1837) and revisited by YEO (1990) in Geraniaceae, which also serve in our analysis to define the two sections.Mericarps separate upwards in sect.Monsonia, while in sect.Olopetalum they separate downwards (see also ZOHARY, 1972, figures 332, 345 and 350).Robustness of columella and mericarp are very variable characters in Geraniaceae (unpublished data) and may be related to dormancy (AEDO & al. 1998).Plumose awn has been considered in the past a significant character to outline infrageneric groups in Monsonia and Erodium (BOISSIER, 1867).
The awn aids both seed dispersal and establishment in the soil (COBELLI, 1892; YEO 1990), as occurs in sect.Olopetalum.Additionally, mericarp devices contribute to mericarp burying in the following aspects: (1) the hygroscopic awn rotates and plants the mericarp; (2) the ridges on the top of mericarp are directed upwards and serve to enable penetration or retention of the mericarp underground; (3) the mericarp bristles are directed upwards, helping retain te mericarp underground; (4) the fusiform mericarp has a sharp callus on its bottom, to enable penetration of the soill.In contrast, plumose awns of sect.Monsonia do not aid to bury the mericarp because they are not sufficiently robust to penetrate in the soil nor do they aid rotation through humidity changes.
A shift from wind dispersal to adhesive dispersal by animals is suggested by phylogenetic reconstructions of Geraniaceae.Phylogenetic analysis of rbcL (PRICE & PALMER 1993) and trnL-F (unpublished data) sequences suggests that the primarily wind-dispersed Pelargonium is sister group to the rest of Geraniaceae.Two main wind-dispersed mechanisms can be envisaged in Geraniaceae.One is present in most Pelargonium mericarps having a tuft of hairs from the basal to medial zone of the tails (similar to a pappus).The other is found in Monsonia, Sarcocaulon and Erodium and consists of a plumose awn.Mericarp structure associated with zoochory mode (S0RENSON, 1986, STEB-  BINS, 1974) seems to be an advanced adaptation that occur independently in Geraniaceae, including sect.Olopetalum.Besides, animal dispersed mericarps are usually larger in Geraniaceae than those of the wind dispersed ones (LEISHMAN & WESTOBY, 1994; GAJEWS- KI 1959KI , 1963)), and this is the case of sect.

Olopetalum.
There is a pattern for cotyledon evolution in which a flat cotyledon has increasingly been folded to conduplicate cotyledons in sect.Olopetalum (YEO 1990).Cotyledon conduplication is also found in Erodium and Geranium, which might have occurred independently.Molecular phylogenetic studies, already in progress, may shed further light on this and depict a far more robust picture of morphological evolution in Monsonia and Geraniaceae as a whole.

Fig. 2 .
Fig. 2. -Flower and fruit structures in Monsonia longipes and M. brevirostrata.a-f: M. longipes (Cufodontis 555, W); a: flower; b: front view of a group of stamens; c: lateral view of a group of stamens; d: transversal section of nectary; e: schizocarp with the five awns partially separated; f: mericarp body; g: surface of mericarp body showing long and short bristles; h-m: M. brevirostrata (Krook 2220, W); h: mericarp body; i: front view of a group of stamens; j: lateral view of a group of stamens; k: schizocarp with the five awns partially separated; 1: flower; m; nectary.

Fig. 4 .
Fig. 4.-Light and SEM micrographs of axillar nectaries with the sepals and the receptacle enlarged forming a pouch.A: Thin-section of Monsonia umbeflata flower showing the cavity formed by sepals and receptacle.The sepal bundle (sb) progress close below the nectary {L-W.Carisso & F. Sousa243, COI).B: Thin-section of M. luederilziana flower showing the cavity formed by sepals and receptacle formed by enlarged sepals which have an appendage to close it (a); the nectariferous tissue (nt) is stained in the surface of the cavity.It is covered by hairs and connected with the sepal bundle (Schlieben 8806, W).C: Thin-section of M.parvifolia flower showing the cavity formed by sepals (s) and receptacle (en) and the nectariferous tissue (nt) {Schlechter s.n., W).D: SEM rnicrograph of nectary of M. parvifoliashowing the cavity formed between the base of a stamens group <st) and the sepals; two walls (w) connect the stamen filaments with the sepals and close the cavity.The nectary is followed by a channel (ch) along the group of filaments, with two rows of hairs (h), which lead the nectar upwards.E: SEM micrograph of nectary of M.parvifolia showing this cavity covered with hairs.F: SEM micrograph of surface ofM.parvifolia nectary showing one stoma (s) and hairs (h) (Schlechter s.n., W).

Fig. 5 .
Fig. 5.-Light and SEM micrographs of staminal nectaries in species of Monsonia showing nectary protuberance without nectariferous tube.A: Thin-section of M. grandifolia flower; the nectaries form a long protuberance with the secretory tissue in all the surface (sn) (H.Rudalis 1342, W s.n.).B: SEM micrograph of base of stamen filaments and nectary of M. natalensis.The nectary form a protuberance at the base of each stamen group (sn) which has a channel (ch) where the nectar rise, being latter retained on the hairs (Kuntze s.n., P).C: SEM micrograph of antisepal side of M. natalensis nectary, showing aperture on the nectary top (ap), nectariferous tissue is only on the antisepal side.The base contains most of stomata; the interior has no stomata (s) serving to retain nectar (Kunlze s.n., P).D: Light micrograph of M. emarginata showing staminal nectaries (sn) and the nectariferous tissue (nt) (Penther 2174, W).E: Light micrograph of M. brevirostrata showing staminal nectaries (sn) and the bundles of stamen (stb) and sepal (sb) (Krook 2220, W).F: Light micrograph of M. nivea showing staminal nectaries (sn) (/,.Kralik 26, MA 628481).

Fig. 6 .
Fig. 6.-Light and SEM micrographs of stamina!nectaries in species of Monsonia showing a protuberance with nectariferous tube.A: Light micrograph of M. longipes flower.The nectaries are protected by an appendage (arrow) attached to stamen filament with a conic cavity inside.The secretory tissue is on the inner surfaces of the cavity (nt) and the appendage (a) (Cufodontis 555, W).B: SEM micrograph of a section of M. longipes nectary showing the nectariferous surface (nt) and the sepal appendage (a) (Cufodontis 555, W).C: SEM micrograph of appendage of M. longipes nectary (a) showing the outer surface (o) of sepal appendage (a) (Cufodontis 555, W).D: Light micrograph of a section of M. longipes nectary showing the secretory tissue on the basal surfaces of the cavity (nt), and the appendage.E: SEM micrograph of inner surface of nectary, which has stomata (stm> (Cufodontis 555, W).F: SEM micrograph of outer surface of nectary, which has no stomata (Cufodontis 555, W).

Fig. 12 .
Fig. 12.-Scanning electron micrographs of mericurp surface of Monsonia sect.Monsonia.A: SEM micrograph of a section of mericarp of M. luederitzutna showing large papillae and pockets (p) surrounding the base of bristles (b).Mericarp wall: mw, and seed testa: t (Schlieben 8806.W).B: SEM micrograph of mericarp surface of M. parvifolia showing pockets rounding the base of bristles (p) (Schlechters.ru,W).C: SEM micrograph of mericarp surface of M. deserticola showing a reticulate pattern with concave cells, and bristles without pockets.{Dinter 6611, P).D: SEM micrograph of mericarp surface of M. hellotropioides, showing pockets (p) rounding the base of bristles (Rechinger 27633, W).R: SHM micrograph of a mericarp wall section with a bristle insertion in M. nivea, showing exocarp (e), schlerenchima region (s), endocarp (en), basal cell of the bristle (be), second cell of the bristle (sc) and tubular cell of the bristle (tc) (Kralik 26, MA 628481).F: Light micrograph of separate exocarp layer of M. nivea fruit showing wavy cells and the bristle insertion.G: SEM micrograph of mericarp surface of M. nivea showing a single type of bristles wich have a truncate lip.H: SEM micrograph of mericarp surface of M. luederitziana showing pockets surrounding the bristles base (Schlieben 8806, W).

Fig. 14 .
Fig. 14.-Strict consensus tree of 9 most parsimonious trees of Monsonia obtained from the analysis of 20 morphological and anatomical characters.Circled numbers indicate bootstrap values from 100 replicates.Solid bars are unambiguous synapomorphies, parallel lines are parallelisms; roman numbers designate clades referred to in the text.

TABLE 1 COMPARISON
OF MAIN INFRAGENERIC TREATMENTS OF Monsonia.SECTION (OR INFRAGENERIC RANK) NAME ARE INDICATED IN EACH COLUMN.SPECIES OF DOUBFUL ASSIGNATION ARE INDICATED BY "?"; SPECIES NOT CONSIDERED ARE INDICATED BY "-"

TABLE 2
THE 20 MORPHOLOGICAL CHARACTERS USED IN THE CLADISTIC ANALYSIS OF MONSONIA .-Species of Monsonia sect.Olopetalum have reticulate pollen with large cells (fig.7G-H),whereas species in M. sect.