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Review article Infrageneric classification of Quercus (Fagaceae) and typification of sectional names KC Nixon LH Bailey Hortorium, Cornell NY 14853, USA University, Ithaca, Summary — The genus Quercus L (the true oaks) is widespread in the Northern hemisphere, in habitats ranging from temperate and tropical forests to dry thorn scrub and semi-desert. As far as is known, all species are anemophilous. The genus is most closely related to Trigonobalanus Forman, Colombobalanus Nixon and Crepet, and Formanodendron Nixon and Crepet, 3 extant tropical mono- typic genera. The oldest unequivocal oak fossils are Oligocene in age, although fossilized catkins and stellate trichomes that may represent earlier Quercus are preserved in Baltic amber, of uncer- tain Early Tertiary age. Trigonobalanoid fossils are known from the Oligocene and Paleocene of North America, and later deposits in Europe. A subgeneric and sectional classification of Quercus that is slightly modified from that proposed by Camus is most consistent with recent phylogenetic analyses within Quercus. Such a classification recognizes 2 subgenera, Quercus and Cyclobalanop- sis (Oersted) Schneider. The latter is restricted to eastern Asia and Malesia. Subgenus Quercus is divided into sections Lobatae Loudon (red oaks: North and South America), Protobalanus (Trelease) Schwarz (intermediate oaks: western North America), and Quercus (white oaks: E and W hemi- spheres). Two groups of white oaks that are sometimes recognized as sections, Ilex (Eurasia), and Cerris (Eurasia) are considered part of section Quercus, but merit subsectional or higher rank follow- ing more complete analyses. Quercus / taxonomy / phylogeny / subgenera / sections Résumé — Classification à l’intérieur du genre Quercus et caractérisation des noms de sec- tions. Le genre Quercus (les vrais chênes) couvre l’ensemble de l’hémisphère nord et colonise des habitats allant des forêts tempérées et tropicales aux formations arbustives et semi désertiques. D’après les connaissances acquises à ce jour, toutes les espèces sont anémophiles. Le genre est proche de 3 genres tropicaux monotypiques vivants :Trigonobalanus Forman, Colombobalanus Nixon et Crepet et Formanodendron Nixon et Crepet. Les restes fossiles les plus âgés datent de l’oligocène, bien que des chatons et des trichomes étoilés susceptibles de représenter le genre Quercus et datés de manière imprécise du début du tertiaire aient été préservés dans de l’ambre de la mer Baltique. Des fossiles trigobalanoïdes datant de l’oligocène et du paléogène en Amérique du Nord et des dépôts postérieurs en Europe ont été reconnus. La classification en sous-genres et en sections, tenant compte des analyses phylogénétiques récentes, est proche de celle proposée par Camus. Cette classification comprend 2 sous-genres, Quercus et Cyclobalanopsis (Oersted). Le dernier n’est représenté qu’en Asie. Le sous-genre Quercus est divisé en 3 sections : Lobatae Lou- don (chênes rouges : Amérique du Nord et du Sud), Protobalanus (Trelease) Schwarz (chênes inter- médiaires : Amérique du Nord occidentale) et Quercus (chênes blancs : hémisphères est et ouest). Deux groupes de chênes blancs souvent classés dans les chênes blancs comme sections, Ilex (Eu-
rasie) et Cerris (Eurasie) sont considérés comme appartenant à la section Quercus; ils mériteraient cependant d’être classés en sous-sections ou à un niveau supérieur après analyses complémen- taires. Quercus / taxonomie / phylogénie / sous-genres / sections INTRODUCTION species of Quercus, Trigonobalanus and Colombobalanus (Manos et al, manuscript phylogeny of Quer- in preparation). The relationships of vari- Recent studies of the (Nixon, 1984, 1989) (Manos et al, KC groups within Quercus are summar- cus ous Nixon, P Manos, manuscripts in prepara- ized in figure 1, based on a combination of tion) have provided the basis for a revised the morphological and molecular data infrageneric classification of the genus. analyses that will be presented elsewhere Quercus is most closely related to the re- (KC Nixon, P Manos, manuscript in prepar- cently discovered tropical genera Trigono- ation). The morphological data set allowed balanus Forman, Formanodendron Nixon greater resolution of among-section rela- and Crepet, and Colombobalanus Nixon tionships, while the molecular data set add- and Crepet (Nixon, 1989; Nixon and Cre- ed synapomorphies for sectional groups. In pet, 1989). Cladistic analysis of 17 mor- general, the results of these analyses sup- phological characters (Nixon, 1984) (KC port recognition of 4 monophyletic groups Nixon, P Manos, manuscript in prepara- of oaks, the Cyclobalanopsis, the Lobatae tion) has been undertaken in combination (the red oaks, subg Erythrobalanus of re- with chloroplast (cp) DNA restriction site cent literature), the Protobalanus (the inter- analyses of 92 informative sites among 33 mediate oaks) and the white oaks in the
of the taxa Camus broad sense (variously referred to as Le- It is recognized. some pidobalanus, Euquercus, or Leucobalanus of Loudon’s important to synonymize some in recent literature). Note that the "Cerris" which published si- sectional names were and "Ilex" groups are not recognized here multaneously. as sections, and may merit recognition as subsections within section Quercus but the limits of these groups in terms of both spe- FOSSIL HISTORY cies and characters is not clear at this time, particularly when the Asian species The oldest unequivocal oak fossils are of Quercus are considered. Because of acorns, staminate catkins/pollen and com- this uncertainty, I have chosen to defer a pressed leaves from Oligocene deposits of subsectional treatment within the white North America (Daghlian and Crepet, oaks until more data are available. 1983; Crepet, 1989; Crepet and Nixon, Because of the general similarity of the 1989a, b; Nixon and Crepet, 1989). Stami- results of recent phylogenetic analyses to nate catkins and stellate trichomes that re- the previous classification proposed by Ca- semble those of modern oaks are pre- mus (1938), and in order to maintain the served in Baltic amber of northern Europe greatest level of taxonomic stability,I have (Conwentz, 1986), but need further investi- followed her classification as closely as gation, because they occur with fruits possible. However, Camus did not always which appear to be trigonobalanoid. adequately search for the earliest names Prior to the the oak Oligocene, lineage at the sectional level in Quercus, and represented by trigonobalanoid fossils is some of the names which she used must consisting of well-preserved fruits and be replaced by earlier names. In particular, infructescences, pistillate and staminate the sectional name of the red oak group inflorescences with in situ pollen, and as- must be changed to the oldest available sociated ’Dryophyllum’ type leaf compres- name, Lobatae Loudon. In addition to the sions (Crepet and Nixon, 1989a, 1989b). names accepted below, lectotypification of While these fossils are not identical with the sectional names proposed by Loudon modern trigonobalanoids, they share ples- (1830, 1835-1838) and others, even though iomorphic features, such as several free they are treated as synonyms here, is im- triangular fruits in a valved cupule, capitate portant in order to stabilize the infrageneric stigmas and cupules arranged along an el- nomenclature of Quercus. In all cases of ongate axis. lectotypification below, an attempt has been made, where possible, to lectotypify Throughout mid- and late-Tertiary de- these names so that names currently and posits of the northern hemisphere, oak leaf widely in use are not replaced. This has compressions and impressions are abun- not been possible in all cases. dant, and many of these, particularly from North America, have been identified as beyond the scope of this paper to Is it close relatives of modern species. Wheth- exhaustively review the history of subgen- er or not the Miocene and Pliocene spe- eric and sectional names in Quercus, but cies are as close to modern species as the synonymy presented below includes all some authors have presumed, it is clear names which have been used extensively. that by this time the oak flora had become I present here an infrageneric classification prominent and diverse, and at least super- of the genus Quercus which broadly fol- ficially resembled the assemblages seen in lows that of Camus, but utilizes Loudon’s sectional names which have priority for modern subtropical and temperate forests.
2-3 years; acorn maturation biennial. Sec- Futher work is necessary to resolve the phylogenetic affinities of these abundant tion Protobalanus. Tertiary oak leaf fossils. CC. Abortive ovules always basal; leaves deciduous to subpersistent, rarely KEY TO THE SUBGENERA persistent for more than 1 year; acorn mat- AND SECTIONS OF QUERCUS uration biennial or annual. Section Quer- cus. A. dis- Stigmas capitate subcapitate to or coid, styles generally terete without adax- TAXONOMIC TREATMENT ial stigmatic groove; staminate catkins OF QUERCUS usually with prominent bracteoles, these subpersistent to caducous; scales of cu- pule in concentric or spiral rings, usually Quercus (oak, encino, chêne) obviously connate laterally to form lamel- lae; east Asian. Subgenus Cyclobalanop- Quercus L, Syst PI ed 2, II, 994. 1753. sis. [for complete synonymy at the generic level, see Camus (1938)]. - Type: Quer- AA. Stigmas usually linear ampliate or broadly ampliate, styles grooved, or with a cus robur L (fide ING) short stigmatic groove extending from the stigma; staminate catkins with inconspicu- Trees or shrubs, flowers monoecious; bracteoles, or these some- ous, caducous wood ring-porous or diffuse-porous; termi- times lacking; scales of cupule various, im- nal buds prominent, quadrangular to pen- bricately arranged and free; widespread in tangular or rounded in cross-section; bud the northern scales imbricate, bud stipules sometimes hemisphere. Subgenus Quer- persistent; axillary buds often closely asso- cus. ciated with and subtending terminal bud; B. Base of leaves spirally arranged, craspedodro- pistillate perianth (perigon) free, forming a skirt or flange; styles usual- mous, mixed craspedodromous or campy- ly elongate, linear-ampliate; endocarp al- lodromous, rarely bronchidodromous, often ways tomentose; cup scales typically flat, with parallel secondary veins, marginal unkeeled; teeth of leaves if present usually teeth (if present) simple, aristate, mucro- aristate or spinose, rarely mucronate. Sec- nate or oblique, 1 associated with each tion Lobatae. secondary vein, or in some species the secondary vein branching and terminating BB. Base of pistillate perianth (perigon) in several teeth; staminate inflorescences adnate to ovary/style bases, not forming a lax-spicate (catkins), clustered at the base of new growth or occurring singly in the ax- flange or skirt; styles elongate and linear- ampliate or short and broadly ampliate or ils of some of the lower leaves, emerging at vernation; staminate flowers single or in cuneate; endocarp tomentose or glabres- cent; cup scales typically keeled or tuber- groups of 1-3 along rachis, subtending culate or both; teeth of leaves if present ar- bracteole prominent and often exceeding istate, pungent, perianth and persistent past anthesis, or mucronate. or inconspicuous and caducous; stamens 6 C. Abortive ovules apical to lateral, (2-12), usually exserted at anthesis, sur- basal; leaves persistent rounding a tuft of simple trichomes inter- rarely appearing
preted as representative of a rudimentary China and southeast Asia (150?); fewer species are found in the western United pistillode: pollen tricolporate (-tricolpate), States (ca 25) and temperate Europe and spheroidal to subprolate or suboblate, ex- ine sculpture generally rugulate or sca- North Africa (8-12?); 1 species is found in brate, often microscabrate; pistillate inflo- northern South America (Colombia). borne in the axils of leaves of rescence usually stiff, with 1- young branches, several partial influorescences, each sub- Subgenus Cyclobalanopsis — tended by a cupule, only the single central (cycle-cup oaks) flower of each influorescence developing; pistillate perianth cupped to campanulate Quercus subgenus Cyclobalanopsis (Oerst- or rotate, shallowly to deeply 5-6 lobed, or ed) Schneider, Handb Laubh,I, 210. 1906. the lobes obscure, basally adnate to the Cyclobalanopsis Oersted (as genus), Bi- ovary or free; ovary 3 (-6+) carpellate, in- - drat til Kundskab om Egefamilien, 69. ferior; styles 3 (-6+), linear or subsessile, 1871. -Quercus section Cyclobalanopsis stigmas capitate to linear-ampliate and ex- Bentham and Hooker, Gen PI III,Ip 408. tending along adaxial stylar suture; fruit an 1880. -Type: Quercus velutina Lindley ex acorn, a single rounded indehiscent nut Wallich, non Lamarck. (fide ING) subtended by a cupule that lacks suture zones and does not separate into valves, Trees or shrubs; bark usually smooth or cupule with external imbricate or concen- furrowed, hard, gray or black, rarely light- tric scales, the 2 lateral abortive flowers of colored; leaves persistent or subpersistent, the partial influorescence within the cu- serrate-toothed, teeth if present entire or pule; fruit maturation biennial or annual, or rarely setate; foliar trichomes mucronate or occasionally ’pseudoannual’ as in some thin-walled and glandular, uniseriate, fas- species of section Protobalanus; endocarp ciculate, multiradiate or rosulate, rarely if sericeo-tomentose to glabrescent, columel- ever thick-walled and/or stellate; staminate la and remnants of the septa of the carpels flowers usually distributed in groups of 1-3 often impressed on the seed, forming irreg- along rachis, subtending bracteole usually ular longitudinal grooves; seed coats usu- prominent and often exceeding perianth ally brownish, adhering tightly to the seed and persistent, staminate perianth often at maturity or adhering to the endocarp regularly 6-lobed; anthers apiculate or re- wall; cotyledons free or sometimes fused tuse; pollen exine sculpture typically rugu- completely: abortive ovules apical, lateral late, often microscabrate; pistillate perianth or basal; cupule scales arranged in con- 5-6 lobed, base adnate to ovary; styles 3 centric rows and partially or wholly connate (-6+), usually linear with an expanded flat laterally, to form concentric lamellae, or im- or subcapitate stigma, the stigmatic sur- bricate and free, sometimes reflexed and face extending only partially along stylar spinose. n= 12. suture or sometimes not extending along suture at all, in any case not forming a Distribution: north temperate and sub- prominent stigmatic groove; stylopodial tropical, tropical montane, and particularly umbo often annulate with 1-3 (-5) distinct in Asia sometimes lowland tropical (subge- rings; fruit maturing the 2 season or in the Cyclobalanopsis); the greatest nus con- centrations of species are in eastern North 1 year, but at least sometimes ’pseudoan- nual’ as in some species of section Proto- America (ca 60), highland Mexico and cen- tral America (150-200), and montane sub- balanus; endocarp sericeo-tomentose, remnants of the septa of the carpels often tropical Eurasia from the Middle East to
podial umbo often annulate with 1-3 (-5) impressed on the seed, forming irregular distinct rings; fruit solitary in each cupule, longitudinal grooves, or subglabrous; seed rounded in cross-section, maturing the 1 or coats usually brownish, adhering tightly to 2 season; abortive ovules apical, or in the seed at maturity or adhering to the en- some species variable in position or basal; docarp wall; cotyledons free; abortive ovules apical; cupule scales arranged in cupule hemispheric, cup-shaped to flat; cu- pule scales variable, spirally or concentri- concentric or spiral rows and partially or wholly connate laterally, to form concentric cally arranged; laterally connate or free. lamellae, often densely vestitured. I follow Camus in her broad interpreta- tion of subgenus Quercus, to include all Distribution: subtropical, montane tropical oak species except the Cyclobalanopsis and lowland tropical east Asia and Malay- group, although American workers usually sia. recognize 3 subgenera in North America. I recognize the possible utility of generic Camus’ classification is compatible with re- rank for Cyclobalanopsis as proposed by sults of phylogenetic analyses. Certain Schwarz (1936). Until careful studies pro- Eurasian oaks (eg Q coccifera) as well as duce stronger evidence that Quercus as Protobalanus are morphologically ’interme- broadly defined is polyphyletic, the conser- diate’ in certain characters between red vative stance of recognizing a single ge- oaks and white oaks sensu stricto, and this nus is appropriate. further supports the closer relationship of these oaks to each other than to Cyclobal- anopsis. If Cyclobalanopsis is included in Subgenus Quercus: (scale-cup oaks) Quercus subgenus, prudence as a recom- mends that the remainder of Quercus be Quercus subgenus Euquercus (Hickel accomodated in a single subgenus. The 3 and Camus) A Camus, Les Chênes. major groups of oaks in North America Monographie du genre Quercus. Vol I. may then be recognized as sections (see 373. 1938 below). Large trees, shrubs sometimes low rhi- or zomatous shrubs; bark variable, from Quercus subgenus Quercus smooth to scally or furrowed; leaves per- section Lobatae (red oaks) sistent, subpersistent or deciduous, entire, serrate-toothed or lobed, teeth if present Quercus section Lobatae Loudon, Hort Brit setate, aristate, pungent or mucronate; fo- 385. 1830. Lectotype (here chosen): Quer- liar trichomes thin-walled and glandular, cus aquatica Wait (= Q nigra L). The 4 spe- uniseriate, fasciculate, multiradiate or ros- ulate, and/or thick-walled and/or stellate; cies which Loudon included in this section staminate flowers distributed singly along are red oaks. This eliminates any possibili- rachis, the single subtending bracteole ty of lectotypifying the section so that it is a caducous or sometimes lacking, staminate synonym of the ’type’ section, the white perianth irregularly or regularly 2-6 lobed; oaks. Thus, this name must stand as the earliest name for the red oaks if they are anthers retuse, or with an apiculate or at- tenuate connective; pollen exine sculpture recognized at the level of section. typically scabrate with obscure or obvious Quercus section perforations; styles 3 (-6+), with expanded Integrifoliae Loudon, Hort stigmatic surface, capitate to linear ampli- Brit 384. 1830. Lectotype (here chosen): Quercus phellos L. ate with an adaxial stigmatic groove; stylo-
late, multiradiate or rosulate, rarely if even Quercus section Mucronatae Loudon, Hort thick-walled and/or stellate; staminate flow- Brit 385. 1830. Lectotype (here chosen): Quercus rubra L. ers usually distributed singly along rachis, subtending bracteole caducous or lacking, Quercus section Rubrae Loudon, Arbor staminate perianth irregularly, often deeply Frut Brit 3, 1877. [1835-]1838. - Type: 2-6 lobed; anthers usually somewhat apic- Quercus rubra L. Loudon’s concept of Q ulate, occasionally retuse; pollen exine rubra was that of the northern red oak, not sculpture typically rugulate and microsca- of the southern red oak (= Q falcata), as brate to scabrate; pistillate perianth 5-6 the name Q rubra was applied by some lat- lobed, the base not adnate to the ovary, authors (eg Sargent, 1922). therefore forming a minute free skirt or er flange, the inner cupule scales often insert- Quercus section Nigrae Loudon, Abor Frut ed beneath this flange; styles 3(-6+), line- Brit 3, 1980. [1835-]1838. - Type: Q nigra ar-spatulate, the stigmatic surface extend- L. Loudon followed Michaux in his concept ing proximally along stylar suture, forming nigra as the blackjack oak (= Q mari- of Q darkened stigmatic groove; stylopodial a landica), but included the real Q nigra in umbo often annulate with 1-3 (-5) distinct this section as Q aquatica. rings; fruit maturing the 2 season, or in several species in the 1 year; endocarp se- Quercus section Phellos Loudon, Arbor riceo-tomentose, remnants of the septa of Frut Brit 3, 1894. [1835-]1838. - Type: carpels often impressed on the seed, the Quercus phellos L. forming irregular longitudinal grooves; seed coats reddish or brownish, adhering Quercus section Erythrobalanus Spach, tightly to the seed at maturity; cotyledons Hist veg Phan 11, 160. 1842. - Quercus free or rarely partially connate; abortive subgenus Erythrobalanus (Spach) Endlich- ovules apical, or rarely in some species er, Gen Plant suppl 4, 24. 1847. - Quercus variable in position or subbasal; cupule subsection Erythrobalanus (Spach) Post scales thin, flat, only rarely keeled or tuber- and Kuntze, Lexicon generum Phaner 474. culate, imbricate, spinescent. never 1904. - Genus Erythrobalanus (Spach) Distribution: restricted to temperate, sub- Schwarz, Notizbl Bot Gard Berlin 13, 8. tropical and montane tropical parts of the 1936. Lectotype (here chosen): Quercus new world, from Colombia, South America rubra L. (1 sp) through central America to forests of southeastern Canada, and westward to subgenus Melanobalanus Engel- Quercus southern Oregon; largely absent from the Trans St Louis Acad Sci 3, 388. man, Rocky Mountain area, except for Arizona 1877. and New Mexico. Large trees, shrubs or sometimes low rhizomatous shrubs; bark usually smooth Quercus subgenus Quercus section or furrowed, hard, gray or black, rarely Protobalanus (intermediate oaks, light-colored; leaves persistent, subpersis- golden cup oaks) tent, or deciduous, entire, serrate-toothed or lobed, teeth if present usually aristate or Protobalanus Trelease, in Stan- setate, a terminal seta often present even Subgenus dley, Contr U S Natl Herb 23, 176. 1922. - on untoothed leaves; foliar trichomes thin- walled and glandular, uniseriate, fascicu- Quercus section Protobalanus (Trelease)
Schwarz, Notizbl Bot Gart Berlin 13, celled rays from the epidermis 21. emerging multicellular glandular uniseri- 1936. - Quercus section Protobalanus together, or ate; staminate flowers with 4-12 stamens, (Trelease) Camus, Les Chênes, vol 1, the anthers apiculate; pollen exine sculp- 157. 1938. - Type: Quercus chrysolepis ture rugulate to scabrate, with nanno-striae Liebm. Both Camus and Schwarz inter- rugulae; (fide Solomon, 1983a, 1983b); preted Trelease’s Protobalanus as a sec- on pistillate flowers 1-3, usually sessile, pe- tion, and attributed this rank to Trelease. duncule sometimes developed; styles Confusion regarding the original rank of short and ampliate to long with ampliate this name apparently arose from ambiguity stigma (Q palmen); fruit maturing in 2nd in Trelease’s presentation of the name in year, but often the fertile branches do not his 1924 monograph. Trelease used sev- grow in 2nd year, so that the fruit may ap- eral infrageneric names that had been pro- pear annual (pseudoannual maturation); posed by earlier authors, eg, Leucobala- endocarp tomentose to appearing gla- nus Engelmann, without reference to the brous, theseed coats usually attached to original authority, publication, or rank at the seed but sometimes attached to the which the names were published. Proto- endocarp; cotyledons furrowed, subequal. balanus was presented in the 1924 mono- graph in a similar ’naked’ manner, leading Distribution: western North America from later authors to believe that this was the southern Oregon, south to northern Baja original publication of the name. However, California, Mexico, eastward to central Ari- the first use by Trelease of the name Pro- zona, and barely into adjacent Chihuahua; tobalanus dates to 1916 in Proc Natl Acad also present on the channel islands of Sci 2, 627, where he clearly referred to it southern California, and the only group of as a subgenus, as well as referring to the oaks present on the islands of Guadalupe type of Protobalanus as Q chrysolepis (loc and Cedros off the coast of Baja California. cit, p 629). Protobalanus was again used Protobalanus is a distinctive group of by Trelease in 1918 (Brooklyn Bot Gard about 5 species, 1 of which (Q chrysolepis Mem 1, 497), and again in Standley’s Liebm) is widely distributed and highly vari- Trees and Shrubs of Mexico, 1922. No de- able. The distribution of this group, which scription appeared in the earlier publica- is restricted to western North America, tions, but in the latter, Trelease included suggests a possible common biogeograph- the name in a key to the species of Mexi- ical history with Lithocarpus densiflora and co, with clear diagnostic characters. The Chrysolepis sempervirens and C chryso- 1922 publication therefore must be consid- phylla of the California region. The latter 3 ered the first valid publication of the name, species are apparently relicts of a previ- and there is no ambiguity in the earlier ously richer Asian element in western publications as to the rank (subgenus) at North America that is no longer prevalent. which the name was intended. Protobalanus is undoubtedly the most in- Evergreen shrubs or trees, bark usually teresting group of oaks in North America scaly and rough (as in various white oaks) from the standpoint of phylogeny and bio- on older branches; twigs tomentose to gla- geography. The phylogenetic affinities of brous; leaves persistent 2 or more years this distinctive and unique group are uncer- coriaceous, glaucous and waxy on the ab- tain, although for the present, Protobala- axial surface, entire or toothed, often spi- nus must be considered a part of the nomi- nal subgenus. They appear to be closely nescent, never lobed as in Q robur, foliar trichomes thin-walled, semi-glandular, sim- related to but intermediate between the red with 2-several fasciculate oaks and the white oaks. In this respect, ple single- or
Protobalanus closely parallels the some- Quercus section Lepidobalanus Endlicher, what intermediate groups of Eurasian oaks Gen Plant, suppl 4, part 2, p 24. 1847, pro that center around Q cerris, Q suber, and parte. Lectotype (here chosen): Quercus Q coccifera. Protobalanus species appear robur L. to be strongly reproductively isolated from the other groups of North American oaks, Quercus section Leucobalanus Engel- as no verified natural or artificial hybrids mann, Trans Acad Sci St Louis 3, 381. are known. 1876. Quercus section Mesobalanus Camus, Quercus subgenus Quercus Monographe Genre Quercus, Atlas I, p 49. section Quercus (white oaks) 1936. Quercus section Euquercus Hickel and Ca- Quercus section Dentatae Loudon, Hort mus, Ann Sci Nat Bot, 9 ser. e III, p 379. Brit 384. 1830. Lectotype (here chosen): 1921. - Type: Quercus robur L. Quercus prinus L. Loudon included a broad array of white oaks, including both Quercus subgenus Heterobalanus Oerst- American and Eurasian species, in this ed, Bidr til Kundskab Om Engefamilien. section. 1871 Quercus section Ilex Loudon, Arbor Frut Trees shrubs: bark smooth,rough, scaly or Brit 3, 1899. [1835-]1838 . Type: Quercus flaky, relatively soft, occasionally hard or ilex L. and furrowed; leaves persistent, sub- deciduous, entire, serrate- persistent, or Quercus section Cerris Loudon, Arbor Frut toothed lobed, teeth if present mucro- or Brit 3, 1730. [1835-]1838. - Type: Quer- nate, pungent, or sometimes on juvenile cus cerris L. growth aristate, or rarely (Cerris and Ilex groups) consistently aristate; foliar tri- Quercus section Albae Loudon, Arbor Frut chomes thin-walled and glandular, uniseri- Brit 3, 1730, 1863. [1835-]1838. Type: ate, fasciculate, multiradiate rosulate, Quercus alba L. or and often thick-walled and/or stellate; staminate flowers usually distributed singly Quercus section Robur Loudon, Arbor Frut along rachis, subtending bracteole cadu- Brit 3, 1730, 1731. [1835-]1838. Type: cous or lacking, staminate perianth regu- Quercus robur L. larly to irregularly, often deeply 2-6 lobed; anthers usually retuse, rarely apiculate; Quercus section Prinus Loudon, Arbor Frut pollen exine sculpture scabrate or rugu- Brit 3, 1730, 1872. [1835-]1838. Type: late-scabrate; pistillate perianth 5-6 lobed, Quercus prinus L. the base adnate to the ovary; styles 3(- 6+), usually abruptly ampliate or dilated, Quercus section Lanatae Loudon, Arbor sometimes more gradually ampliate or Frut Brit 3, 1730, 1920. [1835-]1838. subulate, stigmatic surface extending prox- Type: Quercus lanata Smith. imally along stylar suture, the stigmatic surface often cuneate in shape; stylopodial Quercus section Virentes Loudon, Arbor Frut Brit 3, 1730, 1918. [1835-]1838. umbo usually not annulate; fruit maturing Type: Quercus virens Aiton. in the 1st year, occasionally (Ilex and Cer-
WL (1989) History and implications of Crepet ris) maturing in the 2nd year; endocarp early North American fossil record of Fag- the glabrate or with minute tomentose vesti- aceae. In: Evolution, Systematics, and Fossil ture near apex and base, but obscured by History of the Hamamelidae. Vol 2. ’Higher’ the adhering seed coats, or occasionally Hamamelidae (Crane PR, Blackmore S, (Ilex and Cerris) tomentose-sericeous; col- eds), Clarendon Press, Oxford, 45-66 umellar scar typically not present on lateral Crepet WL, Nixon KC (1989a) Eearliest mega- part of seed or endocarp; seed coats at fossil evidence of Fagaceae: phylogenetic maturity adhering to endocarp, or (Ilex and and biogeographic implications. Am J Bot 76, Cerris) to seed; cotyledons equal or une- 842-855 qual, free, or connate (Virentes and Glau- Crepet WL, Nixon KC (1989b) Extinct transition- coideae); abortive ovules basal; cupule al Fagaceae from the Oligocene and their phylogenetic implications. Am J Bot 76, scales keeled or tuberculate, imbricate, 1493-1505 usually with thickened corky base, some- WL (1983) Oak catkins, Daghlian CP, Crepet times reflexed and spinescent. leaves, and fruits from the Oligocene Cata- Distribution: the most widespread section houla Formation and their evolutionary signif- of Quercus, occurring throughout favorable icance. Am J Bot 70, 639-649 habitats in temperate, subtropical and tropi- Hortus Brittanicus. Loudon J Longman, (1830) cal montane parts of North and Central Rees, Orme, Brown and Green, London America, Europe and (extratropical) Asia. Loudon J (1835-1838) Arboretum et Fruticetum It is clear, based on morphological and Botanicum. Longman, Rees, Orme, Brown molecular data, that the Cerris and Ilex and Green, London groups of oaks are part of the broader Nixon KC (1984) A Biosystematic Study of Quer- cus Series Virentes with Phylogenetic Analy- white oak group, sharing the synapomor- ses of Fagales, Fagaceae and Quercus. Ph phy of basal abortive ovules. Because the D Dissertation, University of Texas, Austin exact relationships of these groups are un- Nixon KC (1989) Origins of Fagaceae. In: Syst certain (Ilex may be paraphyletic to one or Assoc Spec vol 40B. Evolution, Systematics more other groups within the white oaks), and Fossil History of the Hamamelidae. Vol 2 it seems best at this time to recognize only (Crane PR, Blackmore S, eds) Clarendon one section for the white oaks sensu lato. Press, Oxford, 23-43 As more data within the white oaks be- Crepet WL (1989) Trigonobalanus Nixon KC, subsectional classifica- available, a come (Fagaceae): taxonomic status and phyloge- tion will be proposed, and the variation en- netic relationships. Am J Bot 76, 826-841 compassed by the Ilex, Cerris, Virentes, Sargent CS (1922) Manual of the Trees of North Glaucoideae and other groups of white America (Exclusive of Mexico). Houghton oaks can be formally recognized based on Mifflin Co, New York phylogenetic pattern. (1936) Entwurf zu einem naturlichen Schwarz O der Cupuliferen und der Gattung System Quercus L. Notizbl Bot Gart Berl 13, 1-22 REFERENCES Pollen morphology and Solomon AM (1983a) white oaks in eastern plant taxonomy of North America. Am J Bot 70, 481-494 Camus A (1938) Les Chênes. Monographie du (1983b) Pollen morphology and Solomon AM Genre Quercus. 2 vols. Lechevalier and Fils, plant taxonomy of red oaks in eastern North Paris (cited as 1936-1938, but not released America. Am J Bot 70, 495-507 until 1938, fide Stafleu and Cowan, 1976) Stafleu FA, Cowan RS (1976) Taxonomic Litera- Conwentz H (1986) Die flora des Bernsteins, ture. 2nd edn, vol 1. Bohn, Scheltema and Zweiter Band; Die Angiospermen des Bern- Holkema, Utrecht steins. Engelmann, Danzig