TRICHOME MORPHOLOGYIN TEUCRIUM L. (LABIATAE). A TAXONOMIC REVIEW

NAVARRO, T. & J. EL OUALIDI (2000). Trichome morphology in Teucrium L. (Labiatae). A taxonomic review. Anales Jard. Bot. Madrid 57(2): 277-297. The micromorphology of trichomes of 56 Teucrium L. species belonging to the 9 sections of the genus in the Mediterranean área was surveyed by scanning electrón microscopy (SEM) of leaves, calyx, corolla and nutlets. 25 trichome types are described, 12 of them are new. Thin1 Departamento de Biología Vegetal, Facultad de Ciencias, Universidad de Málaga. E-29018 Málaga (Spain). e-mail: tnavarro@uma.es 2 Institut Scientifique, Département de Botanique et d'Ecologie Végétale, Université Mohammed V. BP 703 Rabat (Morocco). e-mail: eloualidi@israbat.ac.ma 278 ANALES JARDÍN BOTÁNICO DE MADRID, 57(2) 2000 walled hairs are the exclusive type found in the corolla and are the most widespread type on the abaxial side of the leaves. Subsessile glandular hairs, 2-4-celled, are found on the nutlet and leaves of the semi-shrubby and paleoendemic species. The presence of short or elongated, generally adpressed simple thick-walled slighüy conical hairs provides an additional character to clarify the boundaries between sect. Chamedrys (Mill.) Schreb, and sect. Polium (Mill.) Schreb. Branched non-glandular hairs are confined to sect. Polium subsect Polium, except for the rare branched hair conical and thick-walled type found in Teucrium barbarum Jahand. & Maire (sect. Chamaedrys) and 7". heterophyllum L"Hér. from sect. Teucrium. This last section is well defined by the absence of simple slighüy conical thick-walled hairs and the glandular hairs in the corolla. Sect. Teucriopsis Benth, is of particular interest for the exclusive presence of branched and peltate glandular hairs on the nutlets surface. Sect. Chamedrys is a homogeneous group, distinguished from the other sections by an indumentum formed only by trichomes types evolved from the simple slighüy conical thick-walled hairs. This section overlaps, in the presence of glandular sub-sessile hair on the nutlets surface, with sects. ¡sotriodon Boiss, and sect. Polium subsect. Rotundifolia Cohén ex Valdés Berm. & Sánchez Crespo. The trichomes type of the calyx teeth, abaxial side of the leaf and latero-posterior corolla lobes can be used as a distinctive taxonomic character at specific and infra-specific level. This study supports Bentham's delimitaüon of sections with the addiüons subequently made by Boissier.


INTRODUCTION
The taxonomic valué of the indumentum and its importance in systematic and phylogenetic relationships is well known in Lamiaceae and such related families as Verbenaceae and Scrophulariaceae (ABU ASSAB & CANTINO, 1987;CANTINO, 1990;METCALFE & CHALK, 1950).
Trichomes are among the most useful taxonomic characters in Teucrium L. Their absence or presence, their typology on the nutlet surface can be used as taxonomic markers in the infrageneric classification of the genus (MARÍN & al, 1994), while the infrasectional classification of sect.Polium is based almost totally on the typology of the trichomes (PUECH, 1984;NAVARRO, 1995).
The dependence on micromorphology for the correct characterization of trichome type, diversity and distribution in plant structures leaves, calyx and corolla and their taxonomic valué as an additional marker at specific and subspecific level has been demonstrated in some Italian, Polish, Slovakian and Moraccan species from sect.However, in spite of their stability as a character (DAVIS & HEYWOOD, 1963), there are no reports on the infrageneric valué of the stability, distribution patterns and diversity of trichomes in leaves, calyx and corolla, particularly in regard to the floral features for pollination such as attraction vectors, néctar guides and closed gullet selective mechanism.Furthermore, the taxonomic valué of trichomes in Teucrium is confused because of the varying terminology used in the past and because none of the previous classifications accommodate the full diversity of the Teucrium trichome spectrum.
Teucrium is a large and polymorphic genus mainly in Europe, North África and in the températe parts of Asia.The basic sectional arrangement of the genus (BENTHAM, 1835) is based mainly on the calyx and inflorescence type undertake both very variable characters.The difficulty of classifying some species into sections and the uncertainty over the affinities of some of their sections would led us to a micromorphological study of the leaf, calyx, nutlets and corolla in the hope that it clarify the confusión sectional boundaries and interspecific relationships (ABU-ASAB & CANTINO, 1993) and demónstrate the taxonomic valué of these micro-characters.
In this study, Teucrium sections are recognized in accordance with BENTHAM'S delimitation (1835) with the additions made byBoissiER(1879).

MATERIAL AND METHODS
This present study is based on field studies as well as herbarium specimens housed at the following institutions (abbreviations following HOLMGREN & al, 1990): B, BC, E, G, MA, MGC, MPU, ORT, RAB and TFC.The list of species and their origin is given in the Appendix.Light and SEM microscope were used.For SEM studies, several samples were prepared, minimum three, the flowers and calyces being fixed whole after critical point technique in a Balzers CPD-020, while the nutlets were mounted directly on aluminium stubs and covered with 24k gold in an ion sputter JFC-1100.After coating, they were observed and photographed by a scanning microscope JEOL JSM-840.
Flowers.We studied the adaxial side of the lower lip, principally the central zone (CZ) located between the basal part of anterior lobe (AL) and the entrance of the corolla tube.The lobes (AL; LL, lateral lobes; LPL, latero-posterior lobes) of the lower lip and the inner side of the corolla tube including the stamen base were analysed and trichome types forming part of the floral features for pollination such as the vector of attractions or néctar guides and closed gullet mechanism were described.The epidemial sculpturing of the corolla lobes were also described.The trichomes of the outer and inner side and margin lobes were described, including the type forming part of the closed tube mechanism in immature calyces.For gynodioecious species the calyx and corolla of male-sterile and cosexuals were observed.
Nutlets.Nutlets were previously observed using a light microscope to ensure that they were of normal size and maturity.
Trichomes.Trichome micromorphology and the structure of leaves, calyx, corolla and nutlets were described and classified.The general classification scheme is based on ROE (1971), but the typological classification of glandular hairs is based on CANTINO (1990), and for most of the categories described, thinwalled and thick-walled groups (HARDIN, 1976) were segregated.
The characters of taxonomic interest in the classification were: presence or absence of the secretory cells, glandular and nonglandular; shape of wall of basal and stalk cells, thin-walled and thick-walled, and presence of the transverse wall cells; number and length of the cells in uniseriate trichomes, unicellular or multicellular; presence or absence of few-armed hairs, stellate hairs, dendritic hairs, vermiform hairs and twisted hairs.In addition, the orientation of the trichomes in relation to the epidemial surface (erect, adpressed), the shape (flexuose, curved, hooked, triangular, conic) and finally the presence/absence of micro-papillae in wall cells were analysed.

RESULTS
The trichome micromorphology of the leaf, calyx and corolla of the following taxa was analysed in 5 species of the sect.Teucrium; all species comprising the sect.Teucriopsis; 4 previously uninvestigated species of sect.Chamaedrys; 5 unstudied species of sect.Scorodonia; 2 of sect.Stachyobotrys Benth.; 2 of sect.Scordium; 5 of sect Spinularia; 4 of sect.Isotriodon; 26 of sect.Polium.Sect.Pycnobotrys Benth.was not studied.The surfaces of 41 nutlets corresponding to otherwise unstudied species were also studied.

Synopsis of trichomes types in Teucrium
Figures 1-4 shows the common trichomes types in the studied species.

Glandular trichomes
These constitute an important taxonomic character of the Lamiaceae and Verbenaceae and form part of the floral specialized features for pollination.For each type, the most significant variation is described.Some of these types are present in other genera oí Lamiaceae whose citación is included.The thin-walled and thick-walled groups are also represented in the clavate glandular trichomes.2a).
E: Conical thin-walled unicellular hairs, also called papillate long cells.More or less elongated with or without micro-papillae (fig.2b).
2.3.Branched trichomes It is known that the same hair type can have  N: Long branched hairs, with short axis and very long thick-walled arms (fig.4d) with long axis (fig.4e).
O: Branched hairs, with short axis, thinwalled slightly crumpled arms densely covered with micro-papillae, correspond to the branched type of F4 (fig.4f).

Distribution oftrichomes
The morphology and distribution of trichomes in calyx, leaves and pericarp of the nutlets is shown in table 1, while table 2 shows the same characters from the corolla.Nutlet sculpturing is show in figure 5.
Section Teucrium.The five species examined fall into two groups, one formed by T. fruticans L. and T. brevifolium Schreb, with H trichomes in the calyx and leaves and another group formed by T. chardonianum Maire & Wilczek, T. pseudochamaepitys L. and T. orientale L. subsp.taylori.(Boiss.)Rech, with mainly F4 and F5 trichomes in the calyx and leaves.This is the only section studied with no glandular trichomes in the corolla.
Section Teucriopsis Benth.This section is very heterogeneous.In T. betonicum L'Hér, the main trichome type is F5.T. heterophyllum show a homogeneous indumentum of J type branched trichome in the calyx and leaves and, of great interest, C 2(3)-armed trichomes in the inner margin of calyx lobes.Sometimes, the many-branched J type can be similar in the shape to the dendroid type (M).
T. abutiloides L'Hér., it is the only species studied which shows a predominance of glandular hairs over all structures this results is according to ANTONES & al. (1995).
The nutlets of T. heterophyllum (fig.5b) show reticulate ridges and the distal part is densely covered by 3(4)-celled long branched thin-walled P type trichomes.This is the only species analysed in the genus in which the branched trichomes are present in the nutlets while T. betonicum (fig.5c) is the only species examined with clavate glandular trichomes Al in the nutlet surface.
Section Chamaedrys (Mill.)Schreb.The species studied in sect.Chamaedrys are characterized by the high degree of homogeneity of trichome type, structure and distribution.
The principal trichome type G2, covers all structures.In T. barbarum, the annulus of the inner side of the calyx is formed of branched P type trichome, as occurs in nowhere else in the genus, T. barbarum represents an exception in relation to the other species with J and Gl on the leaves.
The surface of the nutlets in T. barbarum shows deep fields bordered with thick ridges, more or less completely covered by thinwalled 2(3)-celled F5 trichomes and B2 glandular trichomes, while T. fragile Boiss, and T. webbianum Boiss, (fig.5d) display bordered fields, thin ridges and presence of B2.
Section Scorodonia (Mill.)Schreb.In this section, trichome type varíes between species and within the different structures of the same species.The horizontal position of the broad upper lobe of the calyx, leads to an inversión of the indumentum, so that the previous lobes show the same trichomes as the extemal side of the calyx although in greater abundance.
T G3 hairs observed may be regarded as playing a role in strengthening the spine (fig.4h).
Two corolla types are observed.A resupinate corolla in T. resupinatum, T. decipiens and T. maghrebinum with the patches of F2 in the and a corolla without resupination is T. botrys L., which shows a reduced patch.In most of the species, the base of the long corolla tube is densely covered F2 hairs, which is an exception in the genus.
Section Scordium (Mill.)Rchb.The two species studied show the same type of nonglandular F5 type trichomes covering the outer side of the calyx and leaves, although T. melissoides Boiss, shows thick-walled G2 type hairs in the lobes of the calyx.
The nutlets of T. melissoides (fig.5f) show subsessile glandular B4 trichomes and tend to have a smooth surface.
Section Stachyobotrys Benth.A great diversity of trichomes was observed in the two species studied.F4, Gl and Bl were found on the outer side of the calyx in both species and F4, Bl and A2 with Gl on the leaves of T. collincola Greuter & Burdet.In this species too, G3 in a developing state is seen on the base of muero or spine of the lobes, as in sect.Spinularia.
Section Isotriodon Boiss.The main nonglandular trichomes covering all structures are of the G3 type.
T. rupestre Coss.& Balansa (fig.5h) and T. odontites Boiss, (fig.5i) have no reticulated nutlets with the undulating fields and subsessile glandular trichomes distributed on the surface and one or more in the centre of the sunken fields, T. persicum Boiss, (fig.5j) has the surrounding fields and thick ridges quite deep in these three species.The sculpturing of sect.Isotriodon is similar to that of sect.Strachyobotrys although the ridges in the latter are thick and deep.The presence of B2 in T. rupestre is of interest.
Section Polium (Mill.)Schreb.Trichome type, structure and distribution show high heterogeneity in sect.Polium.In subsect.Polium thick-walled trichomes are the predominant type on the calyx, while stipitate-stellate thin-walled types predominate on leaves.The presence of G3 or F5 is more frequent in hermaphrodite plants than their cosexual counterpart.
The nutlets have no hairs and their sculpturing shows reticulated fields in contact with the inside part of the calyx.
In the species of subsect.Rotundifolia Cohén ex Valdés Berm.& Sánchez Crespo except in T. pyrenaicum L. subsp.pyrenaicum G3 type 6(ll)-celled are the most common hairs on the outer side of the calyx and leaves, generally mixed with A2 of proportional length as oceurs in sect.Isotriodon, except in the case of T. yemense Deflers and T. musimonum Humbert, where the leaves and calyx are covered by vermiform trichomes.T. rivas-martinezii Alcaraz & al., T. cincinnatum Maire, T. thymifolium Schreb, and T. sokotranum Vierh.are the only species from this subsection with G2 type hairs in the calyx and leaves, as oceur in the species of sect.Chamaedrys.The leaves of T. thymifolium and T. sokotranum also show the same G2 type with apical cells elongated on the adaxial side and thick-walled vermiform trichomes on the abaxial side.
The presence of the subsessile glandular trichomes in the nutlets of T. yemense (fig.5k) and the presence of G2 trichomes in T. thymifolium represents a rare character within sect Polium.
In the species studied from subsect.Simplicipilosa S. Puech, only T. charidemi Sandwith shows vermiform trichomes.T. leucocladum Boiss, and T. charidemi has slightly reticulated nutlets and bordered fields with small and very thin ridges.This sculpturing type is rare in sect.Polium.

DlSCUSSION
For the standard classification of trichome type in Teucrium, differentiation into thin and thick-walled provides an excellent taxonomic help.Trichome type, distribution and cover vary widely in the different sections of the genus and in the different structures of the same individual plant, as occurs in others Lamiaceae genera (HUSAIN, 1983;DOROS-ZENKO, 1986;HUSAIN & al., 1990).Variations exist between the outer and inner side of the calyx and between the adaxial and abaxial surfaces of the leaves, and, within the same individual plant, the cover is always more diverse and dense on the outer side of the calyx and abaxial surface of the leaves.
The micro-papillae are irregulary distributed over the epidemial cell of the trichomes as slight ridges or globose shapes.They are always present on all non-glandular hairs in the non-functional trichomes.
The diversity observed in the calyx structures is correlated with zygomorphy; strictly symmetrical or bilabiate calyces showing lesser indumentum variabilty, while strongly zygomorphic calyces show high variability.
In the adaxial surface of the lower lip and corolla tube, trichomes type and their distribution are extremely homogeneous in all species of the same section and provide a additional character at sectional and subsectional level.A specialised arrangement of the epidemial cells on the inner side of the lateral and latero-posterior lobes of the corolla is rare in the genus, and has only been observed in the species with well-developed lobes from sects.Polium and Scorodonia, as has been reported in Melissa L. genus (FAHN, 1979).It is assumed that they play a role in the visual attraction of the visiting insects.
Glandular and non-glandular trichomes from the same plant structure always belong to only one group, thin or thick-walled, although the clavate glandular trichomes of the floral specializations are always of the thin-walled type.
The distribution of the glandular trichomes is clearly correlated with their role in pollination.Al type is frequent in the axils and upper part of the inner side of the calyx lobes and in the apical part of the corolla lobes.Bl are totally absent from the adaxial side of the lower lip of the corolla, but appear on the outer side of the calyx and less frequently on the inner side from the insertion of the annulus of hairs to the margin of lobes.B2 and B4 are only observed on the nutlet surface and leaf surface (adaxial and abaxial side, but more frequently on the latter) but never on the calyx structures, and are most frequent in chasmophyte and paleo-endemic species.B4 is the most common type in Scrophulariales and probably represents an ancestral condition in Lamiaceae (CANTINO, 1990).Branched glandular hairs are rare in the genus, only being found in T. heterophyllum.Glandular trichomes have a taxonomic valué at specific and a subspecific level (MRÁZ, 1998) and their presence or absence in the corolla structures can be used as a phylogenetic character.
The presence of branched hairs in vegetative structures has a high systematic valué, since they are only universally present in the species of sect Polium subsect Polium.They are also present in one rare endemic species of sect Chamaedrys from Morocco, T. barbarum and another isolated endemic species of the Canary Islands, T. heterophyllum.The branched hairs in T. barbarum and 71 heterophyllum are both type J, a type not present in sect Polium.
In sect.Polium subsect.Polium, the branched hairs are generally mixed with simple hairs on the leaves and less frequently on the outer side of calyx.RYDING (1998), comments that the species related to T. polium L. group from the Arabian Peninsula show a clear mixture of the simple and branched hairs, which reflects our findings in T. des-caisnei C. Presl.The presence or absence of branched hairs in the genus has an important infrageneric phylogenetic significance.
Simple thin-walled trichomes are universally present in the genus, forming part of the floral features for pollination, such as attraction vectors or néctar guides, including a closed gullet mechanism, except in sect.Polium subsect.Polium and subsect.Simplicipilosa.F2 hairs form part of the closed gullet mechanism of sect.Teucrium and the néctar guides in sects.Chamaedrys, Scordium, Isotriodon and sect.Polium subsect.Rotundifolia.F5 and G3 form the trichome tuft of the closed gullet mechanism in sect Polium subsect Polium and subsect.Simplicipilosa.
Thin-walled trichomes are the most widespread type on the abaxial side of leaves, occurring commonly in every section except sect.Chamaedrys and only occasionally in sect.Polium subsect.Polium.It is also worth noting that thin-walled trichomes on the adaxial side of the lower lip of the corolla and the abaxial side of the leaves exhibit less intra-sectional variation than other trichome types and are therefore of particular valué in assessing intra-generic phylogenetic relationships.F5 type trichomes are present in Calamintha, Clinopodium, Nepeta and are widely distributed through the sections studied except sect.Chamaedrys and less frequent, in sects.Isotriodon and Polium subsect.Polium.
The basic type simple thick-walled hairs (Gl and G2) are the only type present in all the species frorn sect.Chamaedrys and are completly absent in sect.Teucriopsis and Teucrium.This type provides a good additional taxonomic marker for delimiting the sect.Chamaedrys.The widespread presence of G type trichomes (Gl, G2 and G3) in all the sections except in sects.Teucriopsis and Teucrium may have some phylogenetic significance in Teucrium.This basic type also formed the annulus of hairs on the inner side of the calyx in all the species studied except T. betonicum and T. barbarum.
Nutlets with trichomes represent a primitive character in Teucrium according (MARÍN & al, 1994), showing little infra-generic variation.Trichomes are universally present in sects.Teucrium and Teucriopsis and in some European species of sect Chamaedrys and only in some species from sect Polium subsect.Rotundifolia from N África and SE of Spain.It can therefore reasonably be considered as a character of phylogenetic valué at an infrageneric level.
The systematic relationship between sects.Chamaedrys and Teucrium established by MARÍN & al. (1994) on the basis of the presence of the hairy nutlets in the T. marum group, is confirmed by the results obtained in this study of T. barbarum, which has a combination of the taxonomic characters of the sect.Teucrium, such as the symmetrical campanulate calyx and T. creticum L. inflorescence type (NAVARRO & EL OUALIDI, 1997).In accordance with the results of MARÍN & al. (1994).T. barbarum of sect.Chamaedrys belongs to the group of species of T. marum with trichomes on the nutlets, while T. fragile and T. webbianum belong to the T. flavum L. group.The presence of glandular trichomes in the Mediterranean chasmophytic of sect.Isotriodon, T. rupestre and T. odontites, and the presence of glandular trichomes in T. yemense and nonglandular trichomes in T. thymifolium of sect Polium subsect.Rotundifolia, established, in accordance with MARÍN & al. (1994), a relationship between these sections and sect Chamaedrys.
BENTHAM (1835) considered that sects.Teucrium, Teucriopsis and Pycnobotrys are the most distinct of the genus.MARÍN & al. (1994) and HARBONNE & al. (1986) suggest that sect.Teucrium is totally sepárate from the other sections of the genus.Our investigation of micro-morphological characters makes us agree with these authors and also reveáis the distinctness of the sect Polium subsect Polium, sect.Chamaedrys and sect.Teucriopsis from the other sections.
Sect.Polium is the most heterogeneus section as regards trichome type and distribution.Branched trichomes are the only non-glandular trichomes present in the subsect.Polium.Despite this, the morphological diversity is high and acts as an excellent taxonomic marker at different taxonomic levéis.KASTNER (1989) combined the sect Polium under Üie sect Chamaedrys, but our results agree with Bentham's delimitations of the sections.
Sect.Teucriopsis is a polymorphic section.BENTHAM (1835) included two species, T. hetrophyllum, described under the genus Polyodendron Noe and T. betonicum.KASTNER (1989), added T. abutiloides, a species considered by Bentham under sect.Pycnobotrys.The affinity between T, betonicum and the species of sect.Scorodonia has been mentioned by several authors (BENTHAM, 1848; LINK, 1829).Our results reflect the affinity between T. abutiloides and the species of sect.Scorodonia studied, based on the similar distribution patterns of the glandular trichomes and similar patterns in the nutlets sculpturing.
New infrageneric relationships are demonstrated between sect Chamaedrys and sect Polium subsect.Rotundifolia, based on the presence of the same type G2 trichome in T. freynii, T. thymifolium, T. cincinnatum and T. rivas-martinezii.The taxonomic relationship between the T. sokotranum and T. buxifolium Schreb, groups from the Iberian Península and between T. hijazicum Hedge & King and T. cyprium Boiss, subsp.cyprium mentioned by KING (1988) are confirmed by our study of trichome micro-morphology, while a new taxonomic affinity is observed between T. yemense and T. compactum Clem.ex Lag., on the basis of trichome micromorphology and others morphological characters: inflated calyx, elongated spikelike inflorescence and growth habits.
The varied combination of taxonomic characters in sect.Polium, according to NAVARRO (1995), and the observation of trichome micro-morphology strongly suggest taxonomic affinities between T. cyprium subsp.cyprium, T. hijazicum, T. stocksianum Boiss, subsp.stocksianum, T. yemense and T. sokotranum with the eastern Mediterranean species of the sect.Polium subsect.Rotundifolia.In the case of T. leucocladum, a species similar to those of the Mediterranean región (KING, 1988) there are cióse affinities to the Iberian species from sect.Polium subsect.Simplicipilosa.
A study of trichome micro-morphology permits a better understanding of the relationships between the sections investígated.In most cases, character combinations could easily be used as a means of taxonomic identification at different infra-generic levéis.The classification of trichome micromorphology adopted here considerably enhances the valué of this character within the genus and makes it possible to establish systematic relationships with others genera of Lamiaceae or related families.Variation in the distribution of trichome type in the different sections are of phylogenetic use.This study also supports Bentham's system with the additions made by BOISSIER (1879).