Ecological Flora of theCentral Chilterns

Section 4: Betulaceae

Tongue gall on unripe alder cone

Family: Betulaceae (Birches) 4.1Silver birch Betula pendulaThis tree grows commonly and seeds readily across our area, even onthe clays, although its more natural substrate is drier sandy soil andit is infrequent on chalk. It colonises heathland particularly quickly.It was an early immigrant following the retreat of the glaciers at theend of the Ice Age. Like the plane-tree, the peeling outer layers ofbark help it withstand pollution, so it does well in built-up areas. Inthe C20th particularly it spread widely across the clays.Identification The peeling silver paper-thin layers composing theouter bark make it a very familiar tree, although care has to be takento distinguish introduced American poplars. Saplings have a reddishbark. As an older tree it loses its whiteness at the base of the trunkas the bark becomes deeply furrowed and rugged, although it doesnot reach any great age or bulk. The ultimate twigs are very slenderand hang down (hence pendula). The leaves are small, oval, long-pointed, with uneven serration that tends to alternate smaller andlarger teeth (bi-serrate). The flowers are catkins that producecopious tiny winged seeds spreading all too effectively in the wind.Notable sites It has a presence in almost all our woods, but is rarelya defining or dominant tree. An exception is Sandwich Wood, LittleKingshill, where, after clearance of planted timber, it became thedominant colonising species, even more than ash, and now in partsforms a dense uniform birch-wood. The soil is a very sandy clay (asreflected in the name of the wood). The ground flora contains manyplants and fungi rare in this region, typical of acid soils, such as hardfern and oval sedge, which must be survivors from earlier openwoodland. This wood may well have been managed as wood-pasture bythe monks of Missenden Abbey in medieval times. Nearby isBirchmore Wood (now predominantly beech), which was at the edgeof Wycombe Heath before it was enclosed and largely built over. Itis likely that birch was a major component of such heaths andcommons in our area before the enclosures, at least on the sandierclays typical of parts of the Prestwood and Kingshill region.NVC In the NVC silver birch is shown as occurring at low frequenciesin most woodland types. The exception is W16 oak/birch/wavy hair-grass woodland, confined to very acid soils in the southern lowlands.Sandwich Wood, as it was, and as it is now again developing, wouldprobably fit this profile.Galls The most obvious gall on birches is a large ball of proliferatingtwiglets hanging in the tree and particularly conspicuous in winter, a“witches’ broom” caused by the fungus Taphrina betulina, commonacross the area. 17 other gall-causers are known, as befits the tree’slong-standing as a native. Six of these have so far been recordedlocally: two mites Aceria lissonota and Cecidophyopsis betulae, theaphid Hamamelistes betulinus, & 3 gall-midges: Plemeliella betulicola,Semudobia betulae & S. tarda. The last two gall the seeds and aredifficult to find, but are both common. In addition, the crown gall,caused by the bacterium Agrobacterium tumefaciens, which affectsmany different plants, creates lumpy swellings on birch trunks.Mines Even more leaf-miners are known from Britain on birch (55).Eleven recorded locally are: the agromyzid fly Agromyza alnibetulae;the micro-moths Eriocrania salopiella, Ectoedemia minimella(particularly common), E. occultella, Stigmella confusella, S. lapponica,Caloptilia betulicola (the birch leaf roller), Parornix betulae,

Trunk of 30-year-old tree

Autumn leaves

Male catkins in pollen. Erect female flowers abovewill later lengthen & droop as seed catkins

Phyllocavella ulmifoliella, and Lyonetia clerkella; and the sawfliesScolioneura betuleti (autumn) and S. vicina (spring), the second arecent immigrant, first seen in Ireland in 1942, having mines exactlylike the first, but in a different season.Other ecological associates More species have been recorded inassociation with birch in our area than with any other tree exceptoak, confirming its firm establishment at the heart of the local eco-system, at least on the sandy clays. Most of these records are fromSandwich Wood*, and/or the 30-year-old birch-tree in my garden inPrestwood^. A few others are from other sites (eg Angling SpringWood, Lodge Wood) bordering the Prestwood-Kingshill plateau.These associated species include:Large white-moss Leucobryum glaucum.34 fungi: Amanita citrina (including var.alba)*, A. fulva, A. muscaria* (FlyAgaric, abundant in Sandwich Wood), A. rubescens*; Clitocybe odora*; thewebcaps Cortinarius anomalus*, C. delibutus*, C. triumphans^ and C.violaceus*; Hebeloma crustuliniforme*^ (very common); Laccaria laccata*, L.proxima*; Lactarius glyciosmus*, L. pubescens^, L. rufus*, L. tabidus* (birchmilkcap, abundant in Sandwich Wood), L.torminosus^, L. turpis*, L. vietus”;Leccinum roseofractum^, L. scabrum*^ (brown birch bolete), L. variicolor*, L.versipelle (orange birch bolete, a particular feature of Sandwich Wood);Lenzites betulinus (birch maze-gill); Paxillus involutus (brown roll-rim,abundant under my birch tree, where it often forms fairy rings); Piptoporusbetulinus^ (birch polypore, whose brackets are common on the older trees);Russula aeruginea^, R. betularum*^ (birch brittlecap), R. exalbicans^, R.fragilis, R. gracillima*; Tricholoma fulvum (birch knight); Melampsoridiumbetulinum^ (birch rust); Nectria cinnabarina (coral spot on dead birchwood);and Hypoxylon multiforme on fallen twigs.6 plant-bugs, especially birch shield-bug Elasmostethus interstinctus*^,Elasmucha grisea^, and Kleidocerys resedae^.2 plant-hoppers, Oncopsis flavicollis and O. subangulata. 4 aphids.Lacewing Wesmaelius betulinus^.5 beetles: leaf-beetle Cryptocephalus bipunctatus, two weevils, Deporausbetulae^ (a leaf roller) and Apion simile, and two found in birch polyporebrackets, Cis micans and C. setiger. Four other beetles associated with birchwere recorded before WWII, two of them now Notable B, and may stillexist.12 micro-moths, most commonly Ypsolopha parenthesella and Apotomisbetuletana.20 larger moths, most commonly Large emerald, Buff-tip^, Lime hawk-moth,Lesser swallow prominent, Broken-barred carpet^, Scalloped hazel^, Pebblehook-tip^, Scarce umber^ and Pale oak beauty^. I saw the usually high-flyingOrange underwing once at long grass beneath a birch tree.2 sawflies, Arge clavicornis and A. ustulata.Redpolls are most likely to be seen in winter feeding on birch seeds.Human associations According to Hooke (2010), individual trees wererarely referenced in Anglo-Saxon place-names, although birchwoodsdo so more commonly, no doubt due to the paucity of aged specimens.It features, however, in folklore and its wood was used for timber,young flexible branches for whips (hence "to birch"), and bundles oflong twigs for brooms. One of the first trees to come into leaf, itacts as an early sign of spring.Derivation From Anglo-Saxon berc, itself of ancient origin, as in theSanskrit bhūrja. The Latin betula has the same root.Variation A variety with deeply cut leaves, a sport found in Sweden,is sold as 'Laciniata' and is often planted. There is a young tree inthe churchyard around Great Missenden parish church.

4.2

Sandwich Wood, Little Kingshill - young birchwood

Birch polypore bracket

Mines of Ectoedemia occultella

Mine of Scolioneura vicans

4.3

Silver birch tree showing fine drooping twigs

Crown gall on birch

Variety 'Laciniata'

Downy birch Betula pubescensThere are no records for this species for our area inDruce (1927), but recent records show it occurs quitefrequently in the wetter parts of woods on acidic claysin small numbers, usually with silver birch. It does notseem to be a heathland tree with us, as it is elsewhere.All the specimens I have seen were young trees, so itmay be a recent immigrant or descended from plantedhybrids (x aurata), which are inseparable in the field.Identification The leaves are more rounded and notattenuate at the tip as in silver birch and are moreuniformly serrate, not bi-serrate. Young twigs andleaf-stalks are densely downy, but this is soon lost withage. The bark of older trees is greyish, not the brightwhite of silver birch.Notable sites Lodge Wood is the best place to look.Ecological associates Basically the same as for silverbirch. Leaf-miners seen specifically on pubescenslocally are the moth Eriocrania cicatricella, the sawfliesFenusa pumila and Scolioneura vicina, and the flyAgromyza alnibetulae.

Downy birch leaves

4.4

Downy birch leaves with mines of Eriocrania cicatricella (left) & Fenusa pumila (centre) Downy birch: mine of Agromyza alnibetulae

Hazel Corylus avellanaThe familiar "nut-tree" seldom exceeds a large bush. It is ubiquitous in hedgerows and wood-edges on all soils, andmay also occur within woods and as part of scrub on chalk. It was usually coppiced in the past, either to form adense boundary or as a source of hazel poles, regularly re-cut on a cycle of up to 10 years, so that the boles may beof great antiquity. It was one of the earliest colonising species after the last Ice Age, but numbers have probablybeen increased by deliberate planting in hedgerows in early times for its fruit and coppice.Identification The round leaves, typically 8-9cm across, although larger on new shoots, have attenuate tips andshort white hairs, more or less decumbent, above, and longer soft white hairs beneath on the veins. Twigs andleaf-stalks have dense brown glandular hairs. The long male catkins develop towards the end of the year andbecome bright yellow with pollen in our area about the beginning of February. The female flowers are muchsmaller and inconspicuous apart from their bright red styles that emerge after pollen is shed, ensuring cross-fertilisation. The nuts are encased in two densely white-hairy pale green bracts, hardly overlapping at the baseand exposing most of the nut, which ripens hazel-brown. Fully developed nuts typically 1.9cm long, 1.5cm wide.Notable sites An old coppice stool of 3.6m girth was recorded by Edward Milner by the River Misbourne betweenthe Mobwell and Great Missenden. Former coppiced hazel hedges can be seen in many places, such as the trackpast Andlows Farm and at the back of Binders Industrial Estate, Cryers Hill. It grows abundantly in scrub atPrestwood Picnic Site; in the derelict old orchard beside Widmere Field, just south of the west end of Lodge Lane,Prestwood; and in Rignall Wood.Galls Of the six galls on hazel in Britain, half have been recorded locally: the mites Phyllocoptruta coryli, whichdistorts the catkins, and Phytoptus avellanae, which enlarges axillary buds; and the fly Mikomya coryli.Mines Twenty different leaf-miners are recorded in Britain, of which half are known locally, all micro-moths.Commonest of these in descending order of frequency are Phyllonorycter coryli (nut leaf blister moth), Stigmellamicrotheriella, Ectoedemia minimella, Phyllonorycter nicellii, Parornix devoniella and Coleophora milvipennis.Other ecological associates Two aphids are recorded, the whitish Myzocallis coryli (hazel aphid) underneath theleaves, and Corylobium avellanae, a red-mottled green or brown species with longer siphunculi under young leaves oron the tips of shoots. Brown Soft Scale Coccus hesperidium is common on twigs. Birch Shieldbug (see above undersilver birch) is also found on hazel, along with two other plant-bugs, the common Pinalitus cervinus and Pantiliustunicatus. Green shieldbug Palomena prasina, which can be found on many trees, seems to have a particular affinitywith hazel, on which it is often found in large numbers in late summer. Two lacewings tend to be associated withhazel, particularly Hemerobius lutescens. Seven beetles have also been recorded, most notably the leaf-beetleAltica brevicollis, and the weevils Apoderus coryli (hazel leaf roller) and Curculio nucum (the nut weevil thatdevelops in the fruit and can be a crop pest). The colourful green, yellow and black caterpillars of the sawflyCroesus septentrionalis can strip twigs bare of the leaves in hardly any time at all. Five non-mining micro-mothshave been recorded, and three larger moths, of which the July Highflyer and the Nut-tree Tussock areparticularly frequent. I have also found the pupa of a Small White butterfly on hazel. The hazel dormouse hasbeen recorded in our area a few times, but no established colonies have yet been confirmed.

4.5Toothwort often grows under hazel, as it does in our one local site, the bottom of Kingstreet Lane, LittleMissenden. The moss Ulota bruchii grows locally on hazel. Ten fungi have been recorded in particularassociation with hazel, five toadstools (of which Greenflush Fibrecap Inocybe corydalina and Leccinumpseudoscabrum are the most frequent), and five that grow on living or dead wood, most notably Cinnamon PorecrustPhellinus ferreus, Hazel Bracket Skeleteocutis nivea, Bleeding Broadleaf Crust Stereum rugosum, and HazelWoodwart Hypoxylon fuscum.Human associations The hazel is most celebrated for its edible nuts ("cobs"), although the commercially grown"Kentish Cobs" come from the introduced Filbert Corylus maximus (below) which has larger nuts. Shrubs wereregularly coppiced to provide the flexible poles used in fencing and thatching. Hazel features frequently in oldplace-names and as medieval boundary-markers, often with reference to woods and thickets, so it has always beenabundant. Locally, Hazlemere derives its name from the shrub, although the former village is now a built-upextension of High Wycombe, hazel is no longer prevalent, and the "mere" has gone altogether.Derivation Both Anglo-Saxon haesel and Latin corylus derive from the ancient Indo-European root represented inSanskrit by kosa "case or shell", by reference to the nut that is hazel's chief claim to fame. Similarly the specificname avellana derives from Latin avellare "to pluck". "Cob" occurs in Old English as copp, used for any roundedobject, like the top of a hill, and ultimately from a Flemish or Frisian word with similarly wide connotations,including a round loaf of bread, a stumpy horse, or a head.Varieties The variety "contorta" of native hazel (Corkscrew Hazel), with grotesquely contorted twigs and leaves,is sold in local garden centres and grown in gardens. These are probably of hybrid origin.

Hedge of neglected old hazel coppice, Russells Water

Pupal case of moth Coleophora milvipennis and scattered mining areas nearby

Male hazel catkin, red female flower just above

Hazel nuts, west edge of Hazlemere

4.6

Mines of Phyllonorycter coryli in hazel leaf

Caterpillar of sawfly Croesus septentrionalis in threat position

Filbert Corylus maximaThis SE European species is closely related to our native species andis capable of being fertilised by pollen from C. avellana. It wasintroduced for its larger nuts and has long been grown in orchards inthe region for its fruit, known as Kentish cobs (from its particularfrequency in Kent). It can grow into more of a tree than hazel.Identification The leaves tend to be larger than hazel, typically 12cmacross, but the best distinction is provided by the nuts. These arelarger (typically 2.6cm long, 1.9cm wide) and often completely hiddenby the calyx, which is even longer than the nuts (by around 1cm) andpinches inwards at the tip to further hide them. The calyx is notdivided to the base, the deepest split being to about half-way to thebase (at most two-thirds), and then often overlapping so as to leavevery little of the nut exposed.Notable sites The measurements above were taken from a gardentree and a row of specimens in the hedge bordering Prestwood PicnicSite. One old specimen survives in a remnant of an orchard now partof the garden attached to a private residence in Upper North Dean.It was regularly grown in the former orchards of our area.Ecological associates As for hazel. The mines of Phyllonoryctercoryli, Stigmella microtheriella and Incurvaria pectinea have all beenrecorded locally on filbert.Human associations Grown commercially for its nuts (Kentish cobs).Derivation The Normans knew the filbert as noix de Philibert andprobably introduced it, as it was known in Britain as early as the 14thcentury. They named it after St Philibert because the nuts were saidto ripen about his day, 22 August. In our area, while well-grown bythis date they are probably not fully ripe until a few weeks later.Varieties A purple-leaved variety 'Purpurea' is probably the mostoften sold commercially these days, but I have not seen it in the wild.

Filbert. Leaf has mine of Stigmella microtheriella

4.7Hybrid cob Corylus avellana x maximaHazel and filbert are readily inter-fertile and commonlyform hybrid trees wherever they exist in proximity.There is some difference between sources as towhether Kentish cobs were pure maxima or this hybrid.The existence of former orchard specimens in our areawhich correspond to maxima indicates that some, atleast, of the planted cobs were that species, but gardentrees in the area include true filbert and the hybrid.Identification Intermediate between the parents, thehybrid hazel can show various characters of the two.Examination of local specimens has shown that theleaves are typically 9-10.5cm across. The calyx exceedsthe nut by 5-10mm, somewhat pinched or not, split tothe base at one side, although usually overlapping tovarious degrees, so exposing 40-90% of the nut, whichon average is 2cm long by 1.7cm wide. (This descriptioncorresponds in essential details to that of Wilcox,2013.) Wilcox (pers. comm.) has also found that thecatkins of the hybrid are wider than those of thenative.Notable sites Probably widespread but difficult toidentify if not in fruit. There are specimens in a hedgebordering the field behind Green Lane, Prestwood(which may once have backed a domestic orchard), onNairdwood Lane and at Prestwood Picnic Site, whereboth parents occur. It is also probable that many of ourapparently native hazels, especially near houses and innewly planted hedges, are hybrids. Although advertisedas "native British", many commercially available hazels,even if propagated in Britain, are originally fromcontinental stock that is in fact hybrid.

Hybrid hazel. The leaf at the front has a mine of Stigmellamicrotheriella

Turkish hazel Corylus colurnaOccurs only as a planted tree in Priestfield Arboretum. It is easily distinguished by the very laciniate calyxsurrounding the nut. (Note tent-mines of Phyllonorycter coryli on leaves in the photo below.)

Turkish hazel

Hornbeam Carpinus betulus 4.8As a relatively late invader after the Ice Age this tree has a limited distribution nationally, being native only insouth-east England and there not common everywhere, but in our area it is undoubtedly common on all clay soils. Itwas a favoured tree of hedgerow planters in past centuries because it responds well to laying, and this hasprobably increased its frequency even further, as with hazel. As well as hedgerows it occurs commonly also as awoodland tree, capable of competing with beech in terms of height. It self-sows readily.Identification The characteristic dark and light brown-grey vertical streaks down the trunk make it easilyrecognisable even in winter, although old specimens become deeply ridged. The leaves are similar to beech butsharply bi-serrate around the margins and impressed veins. Like birch and hazel, the male flowers, in March-April,are catkins of yellow-green flowers with brownish bracts. The smaller female flowers have tri-lobed green bractsthat expand later to hide the small nutlet. These are very conspicuous hanging from the twigs in summer/autumnand distinct from any of our other native fruits.Notable sites Many of our hedgerows and wood-edges contain former laid hornbeams - eg Hampden Road oppositeStonygreen Cottages, Mapridge Green and Hobbshill Lanes, the east edge of Lawrence Grove. Occasional pollardsare also encountered. As a woodland component it is particularly frequent in Angling Spring Wood, including someold laid specimens along the southern boundary; it is also frequent in College Plantation, Speen. Hornbeam is notvery long-lasting: the largest so far measured was just 2.6m in girth (copse in centre of Big Park, Great Hampden).Another of almost that size (2.55m) stands at the north-west corner of Lawrence Grove Wood - it already looksspectacularly troll-like although it cannot be more than 200 years. The same wood contains other good specimens.Galls The small number of known galls may reflect the native tree's sparse distribution. A fungus Taphrina carpinicauses witches' brooms, while two mites and one gall-midge cause leaf-galls. Taphrina, the mite Aceria tenella, andthe midge Zygiobia carpini have been recorded locally causing galls on hornbeam.Mines Of the 16 leaf-miners recorded on hornbeam in this country, six (all micro-moths) have been found locally.The mines of Phyllonorycter quinnata and Stigmella microtheriella are very common; P. esperella and tenerella,Parornix carpinella and Bucculatrix thoracella have also been recorded.Other ecological associates Relatively few associates have been recorded locally. Pale aphids on the underside ofleaves Myzocallis carpini are specific to hornbeam. The smooth bark is a favourite of the tree slug Lehmanniamarginata that ascends in wet weather to graze the lichens. Jays enjoy the nuts along with beechmast and acorns,but hawfinches are particularly attracted to the fruits. Just three local moths, apart from the leaf-miners, areassociated with the tree - small white wave, Ypsolopha parenthesella, and Aleimma loeflingiana. There are,however, some uncommon fungi that tend to be associated with hornbeam, all but one of which have been foundunder hornbeam in Angling Spring Wood. The commonest is the milkcap Lactarius circellatus, which is likely toappear at any site where hornbeam grows. Three other milkcaps also occur - L. fluens, decipiens and pterosporus .Also frequent is Leccinum pseudoscabrum.Human associations In Anglo-Saxon times this tree seems to have had little significance and rarely, if at all,appears in place-names. Its hard wood was useful for some items of carpentry, however, and, coupled with itssuitability for laying in hedges, it appears to have become more favoured in the 17th to 19th centuries.Derivation Anglo-Saxon horn and béam is literally "hard" (like horn) "tree". Local Bucks names hay-beech andhorned beech refer to its beech-like leaves and use in hedges (hay) and winged seeds ("horns").

Hornbeam leaves Laid hornbeams marking ancient boundary bank

Hornbeam in fruit

Hornbeam trunk showing white streaks, Peterley Wood

Mine of Stigmella microtheriella (left)

4.9

Old hornbeam, Meadsgarden Wood

Autumn colours of yellow and gold

Tree with witches' brooms Taphrina carpini

Alder Alnus glutinosa 4.10This native wetland tree, typical of riversides ("Alder by the Aqua"), has no native sites in our area, which includesonly the upper sections of streams that usually dry up in summer (and these days are often dry all year). It has,however, been planted in two places beside the River Misbourne and in a plantation beside Angling Spring Wood. Itgrows rapidly but does not reach any great age.Identification The obovate leaves (wider at the tip) and male catkins followed by female cones are sufficient todistinguish this tree from any other natives.Notable sites Two young trees stand in Boug's Meadow beside Link Road car-park in Great Missenden, but theonly mature specimens are older plantings in Abbey Park. The largest of these has a girth of 3.07m.Galls Out of ten gall-causers known in this country, four have been recorded locally - remarkable given the paucityof alder trees. These are the fungus Taphrina alni which creates remarkable red tongues on young cones, andthree mites affecting the leaves: Acalitus brevitarsus, Aceria nalepai and Eriophyes laevis.Mines Of 22 leaf-miners on alder recorded from this country, a remarkable number (10) are known to occur onalder (including planted species, below) in our area. These comprise 9 micro-moths (Stigmella alnetella, Caloptiliaelongella, Incurvaria pectinea, Phyllonorycter falconipennella, P. froelichiella, P. kleemannella, P. rajella, P.stettinensis, P. strigulatella) and one sawfly Heterarthrus vagans.Other ecological associates Four common aphids are associated with alder and may occur locally. Two insects arenamed after alder - the Alder Fly and the Alder Moth; both occur locally but neither is associated particularlywith alder. The fly is associated with water because that where its larvae live, so the fact that alder flies andalder trees tend to occur in the same areas is purely coincidence. The moth may use alder but is equally likely touse any other tree - and, in our area, more likely to do so. A vapourer moth caterpillar was found in 2012 on thealders at Boug's Meadow.Derivation Anglo-Saxon alor and Latin alnus share a common ancient root. The specific name glutinosa "glue-like"refers to the fact that the young twigs and leaves are sticky, unlike its introduced relatives (below).

Alder 100-200 years old already decaying

Tongue gall on unripe cone

Galls of Aceria nalepai

4.11

Male catkins, February

Galls of Acalitus brevitarsus

Galls of Eriophyes laevis

Italian alder Alnus cordataAlien tree from southern Italy planted in severalwoodlands and as an amenity tree. In our area it iscommoner than the native alder.Identification Distinguished by larger flowers andfruit, and glossy leaves that are more or less cordate(cordata) at the base (not cuneate) and pointed,somewhat acuminate at the tip.Notable sites Mixed with other new planted trees inseveral of the Hampden Estate woodlands - Warren,Widnell and Hengrove. As an amenity planting at thecemetery at Cryers Hills, and by the pond in thegrounds of the Chiltern Hospital.

Grey alder Alnus incanaAlien tree planted in a very few places.Identification The leaves are oval, rounded at the baseand pointed, not glossy, more deeply serrate and palerunderneath. The cones have shorter stalks thancommon alder. The bark is somewhat greyer than itscongeners, hence the name.Notable sites There is a recent record fromHughenden, and it is also current at Brickfields,Prestwood.

4.12Hybrid alder Alnus x hybrida (= A. glutinosa x A. incana)This planted amenity tree has been recorded at two sites in our area.Identification A mix of characters of both parents: the leaves are variable, cuneate or rounded, some flattenedat the tip, others pointed, with few veins like glutinosa, but distinctly pale beneath and deeply serrate. The conesare unstalked or short-stalked. (See picture below.)Notable sites Planted by Cockpit Hole, Great Kingshill, and by road in front of Prestwood Picnic Site.Ecological associates Probably as for common alder. The mines of Heterarthrus vagans have been found on thetrees by Prestwood Picnic Site.

Hybrid alder, Cockpit Hole