leaves of berberidaceae (berberis and mahonia) from oligocene sediments, near tepexi de...

Review of Palaeobotany and Palynology 110 (2000) 247–257www.elsevier.nl/locate/revpalbo

Leaves of Berberidaceae (Berberis and Mahonia) fromOligocene sediments, near Tepexi de Rodrıguez, Puebla.

Jose Luis Ramırez a, Sergio R.S. Cevallos-Ferriz b,*a Department de Biologıa, Facultad de Ciencias, UNAM, Ciudad Universitaria, Circuito Exterior, Del. Coyoacan 04510, Mexico DFb Institute de Geologıa, UNAM, Cuidad Universitaria; Circuito de la Investigacion Cientıfica, Del. Coyoacan 04510, Mexico DF

Received 28 June 1999; accepted for publication 7 March 2000

Abstract

From the Oligocene Los Ahuehuetes locality, near Tepexi de Rodrıguez, Puebla, Mexico, five new plant speciesare described based on their leaf architecture. The presence of brochidodromous or acrodromous venation, andsecondary veins forming angular (versus rounded) arcs, are well defined characters in the fossil material that relate itto Berberidaceae. Comparison with the leaves and leaflets of extant and fossil plants allow the recognition of oneMahonia and four Berberis new species. The lack of detailed information on leaf architecture in Berberidaceae limitsthe evaluation of the taxonomic relationships that can be suggested between fossil and extant plants. However, froma biogeographic point of view the presence of these new fossil plants supports the hypothesis of a North Americanorigin of the Orientalis Groups of Mahonia, to which a lineage of Berberis may be added. Furthermore, two of thenew species suggest the dispersal, some time during the Tertiary, of a lineage that today forms the Australis Groupof Berberis from low latitude North America to South America. The movement of the Chortis Block is proposed asan alternative to explain the dispersal of a growing list of plants from north to south in the Americas. Only throughfuture geological and palaeobotanical work can this hypothesis be corroborated. © 2000 Elsevier Science B.V. Allrights reserved.

Keywords: Berberidaceae; Berberis; Mahonia; Mexico; Oligocene; phytogeography

1. Introduction The work of Marroquın (1972) denotes a lack ofinterest in considering the limitations of the pro-posed leaf morphological criteria so as to identifyBerberidaceae comprises a group of shrubs or

small spiny trees, and perennial herbs distributed them (Ahrendt, 1961). Similarly, Mahonia istreated as a section of Berberis by Cronquistin the temperate regions of the Northern

Hemisphere; however, Berberis extends its range (1964), based on the absence of constant morpho-logical differences, or geographic barriers, thatto South America through the Andes and up to

the Strait of Magellan (Cronquist, 1981). Based could help in separating these two taxa.In contrast with these two opinions, leaf charac-on extant plants, Mahonia in Mexico has been

used as a subgenus of Berberis (Marroquın, 1972). ters have been proposed as very helpful in distin-guishing between Mahonia and Berberis (Ahrendt,1961; Schorn, 1961). For example, leaves in* Corresponding author. Fax: +52-550-66-14.Mahonia are always imparipinnate, while inE-mail address: [email protected]

(S.R.S. Cevallos-Ferriz) Berberis they are unifoliate. Other characters may

0034-6667/00/$ - see front matter © 2000 Elsevier Science B.V. All rights reserved.PII: S0034-6667 ( 00 ) 00015-4

248 J.L. Ramırez, S.R.S. Cevallos-Ferriz / Review of Palaeobotany and Palynology 110 (2000) 247–257

help in distinguishing species, but are also useful been interpreted as belonging to the lowest memberof the Pie de Vaca Formation (Pantoja-Alor, per-in establishing geographic distributions (Ahrendt,

1961; Schorn, 1961). sonal communication, 1992). The Los Ahuehueteslocality is 4.5 km north-north-west of the town ofWhile characters with a similar leaf base, apex

or shape are easy to observe in these taxa, the Tepexi de Rodrıguez, in the southern part of thestate of Puebla, Mexico, at 18°35∞30◊N,information on the venation patterns is not known

to the same level of detail. Due to the thickness of 97°55∞15◊W (Fig. 1). The sedimentary sequence isformed by layers of volcanic ash, shale, and finethe leaves of many extant species of both genera

it is difficult to observe venation details with the grained sandstone, representing a lacustrine, orlow energy fluvial environment, where fossil plantsnaked eye. However, an attempt to describe them

can be noticed as the patterns are described as are preserved as impressions and carbonaceouscompressions.enervated, subenervated, widely veined, and reticu-

lated (Ahrendt, 1961). Although the fossil record The stratigraphic relationship of the Pie de VacaFormation with the underlying sequence indicatesof Berberidaceae, based on leaf impressions, is

relatively abundant, comparison of it with extant that its maximum age is Oligocene (Pantoja-Alor,personal communication, 1992). In contrast, thematerial is not as precise as desired, since not all

the details of the venation pattern are preserved results of a recent palynological analysis of theLos Ahuehuetes deposit indicate an Eocene toin the fossils, due to the thickness of the leaves.

The fossil record of Mahonia is larger compared Oligocene age for the sequence (Martınez-Hernandez and Ramırez-Arriaga, 1996).with that of Berberis (e.g., Tanai, 1961; Tanai and

Suzuki, 1963; Becker, 1969, 1972; Axelrod, 1987; Considering the stratigraphic and palynologicaldata, an Oligocene age for the Los AhuehuetesManchester and Meyer, 1987; Wolfe and Schorn,

1990; Liu et al., 1996). Although a report on the deposit is suggested. However, the Oligocene agestill needs to be confirmed by radiometric dating.family suggests its presence during the Cretaceous

(Taylor, 1990), this must be re-evaluated. The fossil plants are represented by detachedand often fragmentary organs, mainly leaves andConfident reports can only be traced in works

dealing with middle Eocene sediments or younger(Collinson et al., 1993).

From the Los Ahuehuetes locality, near Tepexide Rodrıguez, Puebla, Mexico, a distinct assem-blage of Berberidaceae leaves has been collected.In the next paragraphs their leaf architecture iscompared with leaves of extant and fossil represen-tatives. One new species of Mahonia and four ofBerberis are recognised. These new plants do notcompare closely with extant Berberidaceae grow-ing naturally in Mexico. Their presence inOligocene sediments of central Mexico gives sup-port to the idea of Mexico being a secondarycentre of diversification of some taxa of the family.Therefore, their probable biogeographic affinitiesare discussed.

2. Material and methods

Fig. 1. Location of Los Ahuehuetes locality in the Pie de VacaThe fossil plants were collected from a continen- Formation, in the State of Puebla, Mexico, at 18°35∞30◊N,

97°55∞15◊W.tal deposit exposed at Los Ahuehuetes, which has

249J.L. Ramırez, S.R.S. Cevallos-Ferriz / Review of Palaeobotany and Palynology 110 (2000) 247–257

fruits of angiosperms (Magallon-Puebla and Etymology: The specific epithet, martinezii, recog-Cevallos-Ferriz, 1994a–c); remains of fern fronds nises the extensive palynological work done withare rare, and the presence of an earthstar fungus Cretaceous and Tertiary sediments, especially thosewas reported (Magallon-Puebla and Cevallos- of the Pie de Vaca Formation, by Dr EnriqueFerriz, 1993). Martınez-Hernandez.

Morphological observations of the fossil leaves Number of specimens examined: Two.were made with an Olympus SZH stereoscopic Diagnosis: Sessile, orbicular lamina, 18.0–23.0 mmmicroscope and camera lucida. in length, 11.0–16.0 mm in width, and a

The fossil leaves were compared to leaves of length/width ratio of 1.63–1.43:1, rounded andextant plants by consulting a large amount of asymmetrical base; toothed margin with two andliterature, and by direct observation of specimens three large triangular teeth per side, of 1.0–6.0 mmfrom herbarium collections. When similarity with in length, apical tooth more prominent anda particular taxon was noticed, this and closely enlarged (which is incomplete) with 8.0 mm; acti-related plants were surveyed. The collection of the nodromous venation, straight mid-vein, principalNational Herbarium of Mexico (MEXU ) was veins depart with a divergence angle from the mid-especially useful in this stage, the herbarium of the vein (DAMV ) of 23°(14–40°).Department of Forestry, Autonomous University Discussion: In this fossil, details of the high orderof Chapingo, Mexico, was also consulted for com- veins were not observed, except for some ellipticparison between fossil and extant leaves. The ter- areols with a free ending, curved, and non-ramifiedminology used to described the foliar architecture veinlet in the basal portion of the lamina.follows that suggested by Hickey (1973). The most relevant characteristics of Mahonia

All the material used in this study is deposited martinezii are the prominent apical tooth and thein the Palaeobotanical collection of the unevenness of the lateral teeth (Plate I, 2 and 3).Palaeontological Museum of the Instituto de However, a smaller specimen included in this speciesGeologıa, UNAM (National Autonomous

does not have identical characters (Plate I, 4) whenUniversity of Mexico).

compared to the larger specimen, but maintains thesame organisation of the lateral teeth, has a compar-atively larger apical tooth, and actinodromous pri-mary venation. This is one of the most important3. Systematic descriptioncharacters to distinguish M. martinezii fromMahonia simplex (Newberry) Arnold and MahoniaClass MAGNOLIOPSIDAaceroides (Knowlton) Schorn et Wolfe, bothOrder BERBERIDALESdescribed from the Tertiary of the USA. TheFamily BERBERIDACEAEOligocene and Miocene specimens of M. simplex

Genus MAHONIA Nuttall include a large record characterised by its highlyvariable leaflets. However, none of the morphotypesSpecies Mahonia martinezii sp. nov. Ramırez &recognised within this species has such a distinctCevallos-Ferriz (Plate I, 2–4))aspect as the lateral teeth or the apical tooth, asHolotype: Palaeontological Collection of thefound in M. martinezii (Schorn, 1961; Meyer andInstituto de Geologıa, Universidad NacionalManchester, 1997). In contrast, the apical tooth ofAutonoma de Mexico, catalogue No. IGM-PBM. aceroides is larger and may resemble a spine1070 (Plate I, 1 and 2).(Schorn, 1961), while that of M. martinezii isLocality: Los Ahuehuetes locality, of the Pie desmaller and broader. Furthermore, the leaflets ofVaca Formation, on the southern bank of theM. aceroides are more elongated and have moreAxamilpa river, north-west of Tepexi deteeth compared with the new fossil species.Rodrıguez, Puebla, Mexico, at 18°35∞30◊N,

Comparison of Mahonia martinezii with other97°55∞15◊W.Age: Oligocene. fossil species is difficult since their reported variabil-


PLATE I

2–4, Leaflets of Mahonia martinezii; 5–8 Leaves of Berberis lozanofolia; 9–10 Berberis poblana.2 Holotype with acrodromous venation, lateral and apical teeth, IGM-PB 1070, scale bar=5 mm.3 Counterpart of holotype with large apical teeth, IGM-PB 1070, scale bar=Fig. 2: 5 mm.4 A specimen demonstrating variability as compared with the holotype, IGM-PB 1071, scale bar=5 mm.5 Leaf with entire margin, acute apex and acrodromous venation, see contact areas between principal lateral and secondary

veins ones (arrow), IGM-PB 1072, scale bar=2.5 mm.6 Leaf with entire margin, acute apex and acrodromous venation, IGM-PB 1073, scale bar=2.5 mm.7 Leaf with a single marginal tooth, IGM-PB 1074, scale bar=1.5 mm.8 Close-up showing curved arcs formed by the principal lateral vein, IGM-PB 1072, scale bar=1.5 mm.9 Holotype with rounded and mucronate apex, see fusion areas of secondary veins with the principal lateral ones (arrows),

IGM-PB 1075, scale bar=2 mm.10 Close-up showing angular arcs formed by veins departing from the principal lateral vein, IGM-PB 1075, scale bar=1 mm.


ity is large and the characters use to define them plants from Asia. The presence of plants that todayoverlap. This situation may reflect either a fast and grow naturally in China in the Los Ahuehuetesimportant radiation of the group, or a limited locality was noticed before, when Magallon-Pueblaunderstanding of the taxonomic characters used to and Cevallos-Ferriz (1994c) described Eucommiarecognise the species. It is our opinion that a constans Magallon-Puebla and Cevallos-Ferriz.revaluation of the characters used to define the

Genus BERBERIS L.fossil species, based on isolated leaflets ofBerberidaceae, is in order. For example, illustrations Species Berberis lozanofolia sp. nov. Ramırez &of Mahonia simplex from the John Day Formation Cevallos-Ferriz (Plate I, 5–8)(Oligocene), Oregon, by Meyer and Manchester Holotype: Palaeontological Collection of the(1998, plates 6, 7 and 9) show differences among Instituto de Geologıa, Universidad Nacionalthe samples. Their variability is higher than the one Autonoma de Mexico, catalogue No. IGM-PB 1072we have observed in extant material, both, in the (Plate I, 5).general shape of the leaflet and in the venation Locality: Los Ahuehuetes locality, of the Pie depattern. Therefore, a review of the extant species in Vaca Formation, on the southern bank of thesearch of characters with taxonomic stability will Axamilpa river, north-west of Tepexi de Rodrıguez,produce a better supported frame to discuss the Puebla, Mexico, at 18°35∞30◊N, 97°55∞15◊W.fossil material of the family. Age: Oligocene.

Among the plants that grow naturally in Mexico Number of species examined: Four.only Mahonia trifoliolata Morican Lavalle resem- Etymology: The specific epithet, lozanofolia, recog-bles Mahonia martinezii in that both have a promi- nises the great support given to the study of fossilsnent apical tooth. However, the shape of the within the global climate change program in Mexicoterminal leaflets, which are more similar to the fossil by Dr. Socorro Lozano-Garcıa.than the laterals, are distinct from the fossil material

Diagnosis: Elliptic and obovate lamina, 9.0–in having a lanceolate to elliptic shape, an acute

16.0 mm in length, 4.0–5.0 mm in width, and abase, smaller (with relation to lamina size) teeth,length/width ratio of 2.2–3.2; cuneate base with anand in that some leaflets have four teeth per sideangle of 31.5°(26–36°); acute or narrowly rounded(Plate II, 17). The other modern Mexican speciesmucronate apex; entire margin occasionally withdiffer from Mahonia martinezii in lacking lateral orsingle tooth; acrodromous venation; strong, straightterminal prominent teeth (e.g., Mahonia muellerimid-vein, a single principal vein on each side of theI.N. Johnston; Plate II, 18; Plate III, 19).mid-vein departing close to the proximal zone ofMahonia lomariifolia Takeda, a cultivated plant inthe lamina, secondary veins originate from the mid-UNAM, native in China, has basal and lateralvein and fuse with the principal veins, the first onesleaflets very similar to those of Mahonia martineziioriginate at two-thirds of the lamina length and(Plate III, 20 and 21). The second and third pairsimulate notorious enlarged arcs that are parallelof leaflets are especially similar to the fossil materialto the mid-vein.in being sessile, having a very large apical tooth,Discussion: Most of the leaves of Berberis can beand in the uneven number and shape of the lateraldistinguished from the leaflets of Mahonia by theirteeth (Plate III, 21). Variability of the leaflets in M.narrow, acute to cuneate base, and smaller teethlomariifolia helps to understand the variability(with respect to the size of the lamina). Althoughobserved in the fossil material. Leaflets increase indifferent venation patterns exist in Berberis [e.g.,size without modifying their shape from the basepinnate; (Plate III, 22 and 23) a large groupto the middle zone of the leaf. From this point on,of leaves is characterised by having acrodromousthe leaflets increase their length and decrease theirvenation, with two lateral principal veins that typi-width, maintaining the shape of the base, the promi-cally extend almost half the length of the leafnence of the apical tooth, and the unevenness of(Plate III, 24), forming an arc with a stout veinthe lateral teeth (Plate III, 20). The evidence points

towards some links of this fossil plant with the originated from the mid-vein. They also have a


PLATE II

11–14, Leaves of Berberis tepexiana; 15 and 16, leaves of Berberis ahuehuetensis; 17, leaf of Mahonia muelleri; 18, leaflet of Mahoniatrifoliolata.11 Holotype with rounded apex, very small teeth, and decurrent base, see arcs formed by the fusion of secondary and principal

veins (arrow), IGM-PB 1076, scale bar=2 mm.12 Counterpart of the holotype showing length and form of the base, IGM-PB 1076, scale bar=0.9 mm.13 Close-up showing vascularisation of a lateral tooth (arrow), IGM-PB 1076, scale bar=5 mm.14 Close-up showing a tooth, IGM-PB 1076, scale bar=0.4 mm.15 Leaf with marginal teeth, decurrent base, and narrow arcs (arrow), suggesting pinnate venation, IGM-PB 1077, scale bar=

5 mm.16 Counterpart showing a narrowly rounded apex, IGM-PB 1077, scale bar=Fig. 5: 5 mm.17 Leaf showing the arrangement and base characteristics of lateral and terminal leaflets, scale bar=5 mm.18 Terminal leaflet with the larger and narrower apical tooth compared with the lateral ones, primary venation tends to be

pinnate, scale bar=11 mm.


PLATE III

Leaves and leaflets of selected extant Berberidaceae.19 Lateral leaflet of Mahonia trifoliata with less teeth and wider lamina than the terminal leaflet, scale bar=10 mm.20 Leaflet of terminal zone of Mahonia lomariifolia with small lateral teeth, scale bar=10 mm.21 Lateral leaflet of M. lomariifolia with less and larger lateral teeth as compared with the terminal leaflet, scale bar=5 mm.22 Leaf of Berberis serrata with few and large teeth, primary venation is pinnate, scale bar=3 mm.23 Leaf of Berberis vulgaris with numerous small teeth, primary venation is pinnate, scale bar=5 mm.24 Leaf of Berberis micropylla with a mucro and two teeth in the distal part of the lamina, primary venation is acrodromous,

scale bar=2.5 mm.25 Leaf of Berberis heterophylla with acute apex, acrodromous venation, and a single prominent lateral tooth, scale bar=2 mm.26 Leaf of B. heterophylla with entire margin, scale bar=Fig. 25: 2 mm.27 Leaf of Berberis siberica with few and large teeth, pinnate venation with acute secondary arcs, scale bar=2.5 mm.


mucronate (or spiny) apex, and lack a petiole Species Berberis poblana sp. nov. Ramırez &(Plate III, 24–26). Cevallos-Ferriz (Plate II, 9 and 10)

Although Berberis coloradensis Axelrod is mostHolotype: Palaeontological Collection of thesimilar to Berberis lozanofolia, they are different inInstituto de Geologıa, Universidad Nacionaltheir base and apex. The base of the former isAutonoma de Mexico, catalogue No. IGM-PB 1075cuneate and very thin in some samples, while its(Plate II, 9).acute apex always is mucronated. In contrast,Locality: Los Ahuehuetes locality, of the Pie deBerberis lozanofolia has leaflets with rounded, orVaca Formation, on the southern bank of theacute with a tendency to obtuse, apex that lacksAxamilpa river, north-west of Tepexi de Rodrıguez,mucro, and its base while cuneate lacks the typicalPuebla, Mexico, at 18°35∞30◊N, 97°55∞15◊W.expansion of B. coloradensis. The presence orAge: Oligocene.absence of a mucro is considered here an importantNumber of specimens examined: One complete andcharacter, since observations on the extant plantsone apical fragment.suggest that this is a very stable character amongEtymology: The specific epithet, poblana, refers tothe species of Berberis. Another difference betweenthe state of Puebla, where the fossil locality isthe leaflets of these plants is their length/widthlocated.ratio. Furthermore, the length/width ratio of theirDiagnosis: Oblanceolate lamina, 13.0 mm in length,leaflets is different.5.0 mm in width, and a length/width ratio of 2.6:1;Berberis microphylla Forst. from Chile is similarcuneate base with an angle of 36°; rounded mucro-to Berberis lozanofolia in having acute apex, cuneatenate apex; entire margin; acrodromous venation;base, and leaf morphotypes with both entire orstrong, sinuous mid-vein; secondary arcs locatedsingle toothed margin (Plate III, 24). Teeth in B.slightly above the mid-length of the lamina, theirmicrophylla is located near the leaf apex (Plate III,amplitude is asymmetric in each side of the mid-24), while in B. lozanofolia it develops at about thevein, which influences the amplitude of the terti-central part of the leaf length. There is also a greatary arcs.similarity between B. lozanofolia and Berberis heter-Discussion: Although Berberis poblana and Berberisophylla Juss. ex Poir. from the Mendoza Provincelozanofolia share many characters, the presence of aof Argentina. Leaves of this South American speciesmucro in the former is a constant character thatare elliptic and obovate in shape (length/width ratioallows distinction between extant species, and shouldof 2.5–3.7:1), have an acute or mucronate apex, aalso be used to separate fossil species. Both of theselength smaller than 3.0 cm, entire margin, and anew fossil species seem to have closer similarity tosingle lateral tooth located towards the centre ofthe extant South American species, especially,the leaf length (Plate III, 25 and 26). Even thoughBerberis heterophylla, mentioned earlier. This extantthey share these characteristics, only one point ofspecies is the only one within the genus whereunion, and not two as in the fossil, is recognisedjuvenile leaves lack mucro while this is present inwhere the secondary veins connect with the princi-the adult leaves, however, their general shape andpal lateral veins, in a point two-thirds above thevenation pattern are constant through ontogeny. Inleaf length (Plate I, 5). At the present moment thecontrast, the shape of the apex and the secondarysimilarity of B. lozanofolia with South Americanvein arcs is different between B. poblana and B.taxa, especially with B. heterophylla, is importantlozanofolia. These differences support the recogni-since their geographic discontinuity posses an inter-tion of two new species based on the variabilityesting biogeographic problem. This distributionknown from the extant plants of the genus.pattern repeats that of other taxa, and may be

similar to that documented for fossil (Tepexi de Species Berberis tepexiana sp. nov. Ramırez &Rodrıguez, Puebla) and extant (Peru) Haplorhus Cevallos-Ferriz (Plate II, 11–14)(Ramırez-Garduno and Cevallos-Ferriz, 1997), or

Holotype: Palaeontological Collection of theto the disjunct distribution of extant species ofLarrea. Instituto de Geologıa, Universidad Nacional


Autonoma de Mexico, catalogue No. IGM-PB Autonoma de Mexico, catalogue No. IGM-PB1077 (Plate II, 15).1076 (Plate II, 11].Locality: Los Ahuehuetes locality, of the Pie deLocality: Los Ahuehuetes locality, of the Pie deVaca Formation, on the southern bank of theVaca Formation, on the southern bank of theAxamilpa river, north-west of Tepexi deAxamilpa river, north-west of Tepexi deRodrıguez, Puebla, Mexico, at 18°35∞30◊N,Rodrıguez, Puebla, Mexico, at 18°35∞30◊N,97°55∞15◊W.97°55∞15◊W.Age: Oligocene.Age: Oligocene.Number of specimens examined: One.Number of specimens examined: One.Etymology: The specific epithet, ahuehuetensis,Etymology: The specific epithet, tepexiana, refersrefers to the fossiliferous locality, Los Ahuehuetes,to the town of Tepexi de Rodrıguez, whose inhabi-where the material has been collected.tants are distinguished by their interest in properlyDiagnosis: Obovate lamina, 33.0 mm in length,conserving the fossil material.12.0 mm in width, and a length/width ratio ofDiagnosis: Obovate lamina, 8.5 mm in length,2.7:1 (data are complementary from the fossil part6.0 mm in width, and a length/width ratio of 4.1:1;and counterpart, although the apex is not present);cuneate base (35°); toothed margin, very smallcuneate base; serrate margin, more than four largeteeth, hardly distinguishable on the margin, widelyconcave-straight teeth per side (it is not possiblespaced from each other in the distal half of theto observe if there was an apical tooth), pinnatelamina; acrodromous venation, slight distinctionvenation, stout, slightly curved mid-vein, second-between the mid-vein and principal veins, second-ary brochidodromous venation, insertion angle toary veins connecting the mid-vein and the principalthe mid-vein of 30°(16–38°).veins at about half of their total length; severalDiscussion: Berberis ahuehuetensis has the samearcs present near the apex of the lamina.problem as Berberis tepexiana, in that none of the

Discussion: Unfortunately, among the extantspecies available for comparison is similar enough

species available for comparison with Berberis to the fossil. Among the extant plants studied, thetepexiana, none had similar characteristics so as Asiatic species with coarse teeth (e.g., Berberisto suggest a close relationship. The most complete serrata Koehne, Plate III, 22; Berberis sibirica Pall.,monograph of the genus describes the venation Plate III, 27) are more similar to Berberispatterns in a very superficial manner (Ahrendt, ahuehuetensis, even in the venation pattern of a1961). The use of other leaf gross morphological small portion that was well preserved forcharacterisations such as leaf shape, size and comparison.number of teeth, etc., insufficiently distinguishesthe species. However, the available information:an obovate leaf with three to four very small teeth, 4. Discussionwidely rounded apex, decurrent base, and thepresence of arcs formed by the secondary veins The identification of Mahonia and Berberis intoward the apex, strongly suggests that B. tepexi- Los Ahuehuetes in low latitude North Americaana, like Berberis lozanofolia, has links with the broadens the discussion on the evolution of bothSouth American species, and therefore may be genera. The Mahonia simplex complex has beenadded to the growing list of taxa with disjunct suggested based on its fossil record to be andistribution between the Tertiary of low latitude important group that can help clarify the palaeo-North America and extant South American vegeta- biogeography of the Asian Orientalis grouption (Cevallos-Ferriz and Ramırez, 1998). (Schorn, 1961). This group is characterised by

having actinodromous primary venation, a featureSpecies Berberis ahuehuetensis sp. nov. Ramırez &first known from the Eocene plants fromCevallos-Ferriz (Plate II, 15 and 16)Utah (Brown, 1934). In the Oligocene, the group

Holotype: Palaeontological Collection of the increased its diversity toward the mid-continent,but by the Miocene these plants with actinodro-Instituto de Geologıa, Universidad Nacional


mous venation began to diminish. The group was that the Berberis species recognised from the LosAhuehuetes locality may be related to species fromrepresented in British Columbia by Mahonia dead-Asia and South America suggest that diversifica-manensis Fry which also grew during the Uppertion followed at least two directions, in which lowMiocene and Lower Pliocene in Oregon. They firstlatitude North America was important. Certainly,became extinct in the present day Rocky MountainBerberis became extinct in Mexico some time afterarea, being abundant in more humid areas ofthe Oligocene, but before this happened the lineageOregon and Idaho during the Upper Miocene andwith Asiatic affinity had moved in that direction,Lower Pliocene. Post Pliocene records are onlyperhaps following, or along with, the Grouprecognised from the western slopes of the SierraOrientalis of Mahonia. The second group ofNevada in California (e.g., Mahonia cf. MahoniaBerberis with the affinity to South Americansimplex; Schorn, 1961). The presence of Mahoniaspecies must be added to a growing list of taxamartinezii in Los Ahuehuetes extends the distribu-that were present in low latitude North Americation of the group with actinodromous venationduring the Oligocene and today grow naturally insome 2400 km south, demonstrating that the groupSouth America (Cevallos-Ferriz and Ramırez,was well established along the west side of North1998). Their movement from north to south isAmerica during the Oligocene. This new reportdifficult to explain, however, recently it has beensupports the hypothesis of Mahonia species withsuggested that the Chortis Block had an importantactinodromous venation having extended their dis-role in the dispersion of these taxa as it moved totribution first to the north and south of Northits present position along the coasts of low latitudeAmerica, and later, moving to Eurasia (Schorn,North America (Cevallos-Ferriz and Ramırez,1961). The group Orientalis of Mahonia is repre-1998). There are, however, opinions that contrastsented in North America today by a single species,with ours (Landrum, personal communication,Mahonia nervosa (Pursh) Nuttall that inhabits1998). Further palaeobotanical work in low lati-

southwestern United States. tude North America will challenge these hypothesisAlthough Berberis is not as common as Mahonia on the movement of some taxa from north to

in the fossil record, its presence in low latitude south during the Tertiary in the Americas, and theNorth America is no less interesting. The species role of the Chortis Block in dispersing them.so far recognised based on leaf venation patterns,do not allow the proposal of taxonomic relation-ships. However, their presence suggests distribu- Acknowledgementstion processes somewhat different from those ofMahonia. In its movement to the north and west Comments by Dr. D. Dilcher, University of

Florida, Gainesville, and Dr. Z. Kvacek, Charlesof North America there is not much problem toUniversity, Czechoslovakia, improved the manu-understand that both taxa, as members of thescript. Technical assistance by Hector Hernandezsame family, had similar potential for their estab-Campos and Antonio Altamira enhanced ourlishment and diversification, as suggested by theobservations and photography. Financial supportlarge number of species inhabiting the same areasthrough Projects Nos. IN207294 and IN205597 ofin Eurasia. However, their movement to south-Direccion General de Asuntos del Personalwestern North America poses some questions.Academico (DGAPA-UNAM) and 1005PT fromSeveral extant species of Mahonia grow natu-Consejo Nacional de Ciencia y Tecnologıarally in the USA, the genus is very diversified in(CONACYT ) to SRSCF are appreciated.Mexico, and some species extend their distribution

into Central America, with their southern limit inCosta Rica. In contrast, the extant species of

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leaves of berberidaceae (berberis and mahonia) from oligocene sediments, near tepexi de...

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