Oaks of the World

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Classification of Krussmann - - -Current Classification --- Today's trend --- Cyclobalanopsis

Classification of G. Krussmann -1962 - (after Prantl)

SUB-GENUS 1 : Cyclobalanopsis (Oerst.) Schneid.
Cupule with concentric rings made up of fused scales; leaves entire or weakly toothed, leathery, evergreen; style short, broader at apex; acorn maturing in 1 or 2 years; aborted ovules near the apex of the fruit; (See the Classification of Menitsky)
= myrsinifolia, oxyodon, stenophylla, glauca, acuta, lamellosa

The cup-scales are not fused into concentric rings; leaves deciduous or evergreen, entire or lobed, apex and lobes acute and bristle-tipped; style straight, elongated; acorn maturing in 2 years (except Q.agrifolia), with thick péricarp, hairy inside; appressed scales; aborted ovules at the apex of the fruit ;

SECTION PHELLOS : leaves most often entire, oblong lanceolate, rolled inside the bud, red or yellow in autumn;
= phellos, imbricaria, laurifolia, incana

SECTION NIGRAE : leaves oboval, wider near apex, with 3-5 lobes at apex or entire, folded in the bud;
= nigra, marilandica, arkansana

SECTION RUBRAE : leaves with pinnatiform lobes, not wider near apex; lobes most often toothed, with bristle tip;
= laevis, falcata, ilicifolia, palustris, georgiana, velutina, rubra, shumardii, texana, coccinea, ellipsoidalis, kelloggii

SECTION STENOCARPAE : leaves evergreen, entire or toothed;
= agrifolia, wislizeni

The cup scales are not fused into concentric rings; leaves deciduous or not, lobed or toothed, with or without bristle tip; style sharp, subulate; acorn maturing in 1 or 2 years; inner surface of nut shell glabrous; cup scales appressed or free; cupule glabrous inside (except Q.chrysolepis ) ; aborted ovules at the base of the fruit ;

SECTION CERRIS : leaves dentate or serrate, with mucronate apex; style subulate, sharp, straight or curved; cup scales elongated, free and recurved, sometimes straight near apex of the cup;
= variabilis, acutissima, castaneifolia, libani, trojana, macrolepis, cerris

SECTION SUBER : style sharp, straight or recurved; cupule with scales free or weakly appressed; fruits maturing in 1 or 2 years; evergreen ;
= coccifera, calliprinos, suber, alnifolia, semecarpifolia, engleriana, leucotrichophora

SECTION ILEX : leaves evergreen, thick, leathery, entire or dentate; fruit maturing in 1 year; style short, rounded ; cup scales appressed;
= phillyraeoides, ilex, chrysolepis, virginiana

SECTION GALLIFERA : leaves with dentate lobes, sometimes entire; style short, rounded; cupule with small, appressed scales;
= fruticosa, lusitanica, infectoria

SECTION ROBUR ; dark bark, deeply furrowed; leaves dark green above; cup scales small or large, appressed or remotely free;
= pontica, canariensis, macranthera, frainetto, pyrenaica, pubescens, petraea, iberica, dalechampii, robur, hartwissiana, polycarpa, pedunculiflora

SECTION ALBAE : bark light grey, peeling into thick plates; leaves light green, often glaucous, purplish or orange brown in autumn; cup scales small and appressed, sometimes large and free;
= alba, lobata, garryana, gambelii, stellata, lyrata, macrocarpa, bicolor, michauxii, prinus, prinoides, aliena, muehlenbergii, fabri, glandulifera, mongolica

SECTION DENTATA : leaves deciduous, very large, dentate; acorn maturing in 1 year; cup scales free, straight, spreading; bark deeply furrowed;
= dentata, yunnanensis

Current Classification

1/ Sub-genus Cyclobalanopsis Oerst. 1867

Cupule with concentric rings of fused scales; all species in Asia ; (See the Classification of Menitsky)

2/ Sub-genus Quercus Hickel & Camus
Cupule with scales not fused;

A // Section Quercus (= section Leucobalanus = White Oaks)
North America, Mexico, Central America, Eurasia, Eastern Asia, North Africa
- evergreen or deciduous
- acorn maturing in 1 year
- endocarp glabrous
- aborted ovules near the base of the fruit
- lobes of the leaves and teeth, if present, without bristle tip
- styles short and enlarged
- cup scales most often thick and tuberculate or convex, more or less downy
- cupule glabrate inside
- acorn generally sweet
- bark light grey or brown, becoming scaly and rough
- wood light beige, with fine texture
- cup scales with thick base
- trichomes conspicuous, rather different from one species to other;

a - leaves lobed
- glabrous
- or pubescent

b - leaves toothed
- 5-8 pairs of lateral veins not all ending in a tooth
- or 9-13 pairs of lateral veins all ending in a tooth

B // Section Lobatae (= section Erythrobalanus = Red/Black Oaks)
North America, Mexico, Central America, South America (Colombia only)
- evergreen or deciduous
- leaves lobed or not, teeth if present usually bristle-tipped
- acorn maturing in 2 years (except Q.agrifolia)
- inner surface of nut shell tomentose
- styles linear, spatulate
- aborted ovules at apex of the fruit
- cup scales thin and wide, flat
- bark smooth or furrowed, blackish brown
- trichomes, if present, large and sometimes tufted; but not very different from one species to another;
- acorn generally bitter
- wood red brown, with coarse texture

a - leaves entire

b - leaves lobed
- with hair tufts (at axil of secondary veins) very conspicuous
- or without conspicuous axillary hair tufts
- 7-11 lobes, dull above, glaucous beneath
- or 5-9 lobes, bright above, light yellow grey beneath

C // Section Protobalanus (= Intermediate Oaks, Golden Oaks)
South-western U.S.A., North-western Mexico
- evergreen
- leaves entire or toothed; teeth generally spinose
- acorn maturing in 2 years
- aborted ovules apical to lateral
- styles short and enlarged
- cup scales thick and tuberculate
- nut with inner wall tomentose
- bark greyish or reddish brown, scaly to smooth, sometimes furrowed
- trichomes most often large, golden yellow grey, not very different from one species to another

This Classification is the one of American Botanists; in Europe, the classification of Quercus is more developed, including especially sections of sub-genus Quercus according to A. Camus; for Cyclobalanopsis there is no differences; here is the 'European' classification most often used:

1/ Sub-genus Cyclobalanopsis
Evergreen leaves, entire or toothed, but never lobed, shiny green above; cup with connate scales, arranged into concentric rings; all species in Asia. (See the Classification of Menitsky)

2/ Sub-genus Quercus
--- Section Quercus (= Lepidobalanus)
styles short, broader at tip; thick, subsessile stigmas; cup with scales more often short, appressed; aborted ovules at  base of fruit; basal scar nearly flat; acorn rippening in 6 months, soft or a little bitter; endocarp glabrous; America, Asia, Europe.
    _ deciduous leaves
    _ persistent leaves

--- Section Mesobalanus
styles long, broader at tip; thick stigmas; aborted ovules at base of fruit; cotyledons usually free; basal scar almost flat; acorn rippening in 6 months, bitter; Europe, Asia, North Africa.

--- Section Cerris
styles long, linear with narrow tip; cup with long scales sometimes reflected; acorn rippening in 18 months, strongly bitter; aborted ovules at base of fruit; scare more or less raised; endocarp glabrous or slightly pubescent; cotyledons likely connate; Europe, Asia, North Africa.
    _deciduous leaves
    _ persistent leaves

--- Section Protobalanus
styles short, broader at tip; broad, spreading stigmas; aborted ovules lateral or basal; cup with short scales; acorn rippening in 18 months, very bitter; endocarp pubescent. North America.

--- Section Lobatae (= Erythrobalanus)
styles long, broader at tip; cup with shot scales; aborted ovules usually at apex or fruit; acorn rippening in 18 months, very bitter; endocarp woolly; North America, Central America, South America.
    _deciduous leaves
    _ persistent leaves

Recent studies of Thomas Denk & Guido Grimm (Department of Paleobotany, Swedish Museum of Natural History, Stockholm) in 2009 and 2010 (*), concerning pollen characteristics and nuclear markers (ITS and 5S-IGS) of some oaks of Western Eurasia, clearly demonstrate the reality of two clades within the Genus Quercus : a clade comprising the Groups Cerris, Cyclobalanopsis and Ilex and an other clade comprising the Groups Quercus, Lobatae and Protobalanus.
Within the Cerris-Cyclobalanopsis-Ilex clade, the Groups Cerris and Ilex are very closely related, and the Ilex Group becomes much more important than in earlier classifications, in inheriting many species from the traditional Cerris Group; in the Quercus-Lobatae-Protobalanus clade, the Quercus Group appears to be derived from Protobalanus, and the Lobatae Group from the Quercus Group.
The transfers of species from one Group to an other one are particularly important between the Cerris and Ilex Groups, and the "new deal" according to Denk & Grimm is :
1/ Cerris Group: Q. acutissima, brantii, castaneifolia, cerris, libani, macrolepis, suber, variabilis
2/ Ilex Group: Q. acrodonta, alnifolia, aquifolioides, aucheri, baloot, baronii, coccifera, cocciferoides, dilatata, dolicholepis, engleriana, franchetii, gilliana, guyavifolia, kingiana, lanata, leucotrichophora, lodicosa, longispica, monimotricha, pannosa, phillyreoides, rehderiana, semecarpifolia, senescens, spinosa.

- Significance of Pollen Characteristics for Infrageneric Classification and Phylogeny in Quercus (Fagaceae), 2009
- The Oaks of Western Eurasia : Traditional Classifications and Evidence from two Nuclear Markers, 2010