Page 1 The Taxonomic Status of Gladiolus illyricus (Iridaceae) in Britain Aeron Buchanan ...

59 Pages·2007·3.08 MB·English

The Taxonomic Status of
Gladiolus illyricus (Iridaceae) in Britain
Aeron Buchanan
Supervisor: FredRumsey,NaturalHistoryMuseum,London
Athesissubmittedinpartialfulfilmentoftherequirementsforthedegreeof
MasterofScienceofImperialCollege,London
Abstract
FirstnoticedofficiallyinBritainin1855,Gladiolusillyricus(Koch)presentsan
interesting taxonomic and biogeographical challenge: whether or not this isolated
northern population should be recognized as a separate sub-species. Fundamental
conservationissuesrestontheoutcome. Here,theinvestigationintotherelationship
oftheG.illyricusplantsoftheNewForest,Hampshire,toGladiolusspeciesacross
Europe,northernAfricaandthemiddleeastisinitiated. Twochloroplastregions,one
in trnL–trnF and the other across psbA–trnH have been sequenced for 42 speci-
mens of G. illyricus, G. communis, G. italicus, G. atroviolaceus, G. triphyllos and
G.anatolicus. Phylogeneticandbiogeographicaltreatmentssupportthenotionofan
east–west genetic gradation along the Mediterranean. Iberia particularly appears as
a zone of high hybridization potential and the source of the New Forest population.
AlignmentwithsequencesobtainedfromGenBankgivestrongsupporttotheclassic
taxonomyofGladiolusbeingmonophyleticinitssub-family, Ixioideae. Comments
onthesechloroplastregionsforbarcodingarealsogiven. Inconclusion,thegenetic
localization of Britain’s G. illyricus population as an extremity haplotype suggests
thatitcouldwelldeservesub-speciesstatus.
Contents
1 Introduction 2
2 Background 4
3 MaterialsandMethods 8
4 ResultsandDiscussion 15
5 Conclusions 26
Appendices 28
References 56
1.Introduction G.illyricusinBritain
Figure1: G.illyricusflowerspike.
Photograph: Fred Rumsey, Denny Wood,
NewForest.
1 Introduction
The study of Gladiolus illyricus (Koch) is particularly pertinent at this time. It is a
medium-sized flowering monocotyledon with a Mediterranean distribution, but with one
important exception: the small yet significant, and now declining population in the New
ForestofHampshire,hereintheBritishIsles.
The natural history of G. illyricus in the UK, until as recently as the 1950s, ranges
from being unclear to unknown. The first recorded sighting was on the Isle of Wight in
1855, with notes of its presence in the New Forest appearing soon thereafter. The origins
ofthispopulation,intheextremenorthofthespecies’range,immediatelybecameapoint
of debate. Was the arrival part of a natural progression northwards or was it an artificial,
human-mediatedintroduction?
Today, the continuing survival of G. illyricus in the New Forest appears fragile, mak-
ing the above an important question. It is currently a protected Schedule 8 species and
so protected under law by the Wildlife and Countryside Act, 1981, but with its endemic
statusunresolved,itremainsonthewaitinglistofCheffingsandFarrel(2005)∗. Thewait-
ing list is populated by “taxa for which questions still remain over taxonomic validity or
endemic status.” Indeed, the example of such a taxon given by the authors is G. illyricus
ssp britannicus. This state of conservation limbo is unsatisfactory, for if the endemic sta-
∗‘The Vascular Plant Red Data List for Great Britain’ is part of the Joint Nature Conservation Com-
mittee’s Species Status project, which is used to inform the statutory five-yearly review of Schedules 8
species.
2
1.Introduction G.illyricusinBritain
tus is rejected then much demanded conservation resources can be redirected elsewhere.
However,ifitisconfirmed,afullermoreconcertedeffortwouldbejustified.
The issue of the British nativity of G. illyricus is theoretically inseparable from the
suggestionthatthepopulationintheNewForestshouldbedesignatedasbeingaseparate
subspecies, G. illyricus ssp britannicus. This study was born with the desire to resolve
the taxonomic status of G. illyricus and hence shed light on the natural history of the
New Forest population. Resolution would thus make clear the level of impetus required
ofconservationefforts.
An outline for a study to answer the question has been proposed by Lockton (2006);
thatis,todemonstrate:
1. theexistenceofaneast–westgeneticgradation
2. thatthegradationiscorrelatedtonaturaldispersalrates.
3. thatthereisspeciationwithinthatgradation.
4. thattheBritishplantsaresufficientlydistinct.
5. thattheybelongtoadistinctivesemi-naturalvegetationhabitat.
The ecological investigation, that can make clear the issues of the fifth point has al-
ready started, most notably by Stokes (1987). This study begins the molecular investiga-
tionoftheG.illyricuspopulationoftheNewForest,andhencestartstoaddresstheissues
ofthefirst,thirdandfourthpoints.
TheworkbeganwiththeimportantgroundingstepofplacingtheEuropeanGladiolus
speciesintoawidercontext. GladiolusisoneofthelargestgeneraintheIridaceaefamily,
with possibly as many as 300 species. Almost all of these grow in sub-Saharan Africa
(Goldblattetal.2001);lessthantwentyspeciesareendemictoEuropeandneighbouring
countries. Support for the monophyletic status of all Gladiolus is needed to be able to
rely on existing work that assumes the long standing taxonomy. After the broad initial
analysis, the project then focussed on the inter-relations within Europe, which were then
exploredwiththeaboveframeworkinmind. Sadly,thefullanswercannotbegivenhere:
limited time restricted the scope of what was achievable. However, important insights
into the wider situation are revealed, providing some answers and raising significant new
ones,thusinformingfutureresearch.
3
2.Background G.illyricusinBritain
Figure 2: An example of G. illyricus from
the herbarium at Reading University. This
isaNewForestplant,collectedin1960.
2 Background
The first systematic study of Gladiolus illyricus (Koch) growing in the UK did not start
untilalmostonehundredyearsafteritwasfirstofficiallynoticed. Assuch,ourknowledge
ofitsdistributionandecologyisverysparsefortimesbefore1950,whenBowmanstarted
the surveying of the New Forest for this purpose (Rand, 2005), and almost completely
blank for anything before 1855, when Mrs Phillipps of the Isle of Wight made the first
record of its growing in the British Isles (More, 1862). According to Townsend (1904)
thefirstmainlanddiscoverywasin1856byRev.W.H.Lucas.
From the mid to the end of the 19th century, the story seems to be one of undirected
specimen collection with the occasional serendipitous discovery of new sites. The Natu-
ralHistoryMuseum’sBritishHerbariumholdsthirtyninespecimensfromthisperiod(the
firstbeingthe1858sheetsofJ.T.Boswell-Syme),allcollectedfromwithintheNewFor-
est (v.c.11), seldom with a more detailed description of location than “near Lyndhurst”.
Accompanying notes are generally sparse as well, although Rand (2005) points out that
descriptions of habitat, beyond “amongst bracken”, were sometimes made. The most
detailed of these are by Dyer and Trimen (1864), but they worked on only two sites in
the New Forest, within less than 3km of each other. Later, Townsend (1904) compiled a
summary of the New Forest locations where it had been found, describing three almost
distinct areas of modest size, all within 6km of Lyndhurst. Crucially, Pope etal. (2005)
4
2.Background G.illyricusinBritain
notes that it was also found near Ensbury, Dorset (v.c.9) around 1874 and collected trice
more from the Isle of Wight in 1872, 1897 and 1931, although the last collection was
rather haphazard. The plants seems to have then received little attention from the turn of
the century until the systematic surveys of Bowman from the 1950s onwards, Hamilton
in the 1960s and Everett in the 1980s (Rand, 2005), as well as Stokes (1987). From their
foundational reports and the continued efforts of the New Forest Study Group, we are
now fairly certain of the full extent of the sub-populations growing in the New Forest.
The widespread activity of botanists across Britain means that we can now be sure that
G.illyricusnolongergrowsoutsidethisarea. Thecurrentrange,whilestillsmall,issev-
eral times larger than that investigated by botanists at the turn of the century, spreading
upto12kmfromLyndhurst.
What the actual distribution was in those early years is almost impossible to deduce,
butitseemsreasonabletosurmise,withsub-populationsgrowingoutsidetheNewForest
at the time, that it was more consistently widespread then, than it is today. However, this
isapivotalhistoricfactorforthequestionofG.illyricusbeingendemicintheNewForest:
care must be taken before assumptions are made. Was the sudden start of botanical inter-
estinthemiddleofthe1800sperhapsaresultofacontemporaryintroductiontothesouth
coast from a continental population? I believe not: it is most likely due to artifacts of
historical circumstances and not because of any events or trends belonging to the plants
themselves over the period in question. Indeed, Mrs Phillipps did not luckily stumble
uponthesingularoccurrenceofG.illyricusontheIsleofWight,butratherthatthe“Wild
Gladiolus”planthadbeengrowinginthewoodsatShanklin,thenearbytown,foratleast
a generation (More, 1862). It is quite possible that, had local people written of the flow-
ers that they commonly saw, or such notes more widely disseminated, records of many
plants would have appeared much earlier. Martin Rand (2005) makes a good case for the
existenceofG.illyricusintheNewForestbeforethefirstrecordsappeared. Hepointsout
thatmanyspecies,clearlynativeintheNewForest,werenotofficiallynoticedasgrowing
there for a very long time (Carex montana: 1876 and Gallium constrictum: 1924, for
example). He adds to that a description of the difficulty of finding G. illyricus colonies,
even when in flower. Another possibly relevant issue is that access to the New Forest
became easier after the railway through it opened in 1847. Furthermore, Rand collects a
variety of ecological observations to support the idea that G. illyricus has been in Britain
for some time. Despite its restricted distribution, it appears in a range of ecotones with a
varietyofassociations,noneofwhichareguaranteed. Also,itseemstobareaninteresting
relationshipwithsemi-naturalhabitats(somedatingbackthousandsofyears),towhichit
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2.Background G.illyricusinBritain
isseeminglywelladapted. Overall,astrongsenseoflong-termnaturalizationisgivenby
what we do know, although the evidence frustratingly does little to dismiss the neophyte
hypothesisoutright. However,thenotionofaveryrecentintroductioncanbedisregarded:
that there was a prolific dispersal of a plant sensitive enough to just about immediately
fallintodecline,orthattherewassomeartificial,yetpersistentefforttospreadtheflower
acrossHampshirearehighlyimprobable. Itseemscertain,therefore,thatitdidnotarrive
just in time for the botanists getting off the first trains ever to arrive at Lyndhurst, but has
itbeenherelongenoughtobeconsiderednative?
ThedebateontheendemismofG.illyricusstartedalongsidethefirstreportsofitsdis-
covery. Alexander More published his opinion in the article revealing the 1855 specimen
(More, 1862). He was convinced that it was indigenous to Britain: the remoteness of the
IsleofWightlocation,thelackofanyknowngardencultivationsandthesimilarityofthe
growing environment between the plants in the UK with those undisputable natural pop-
ulations in north western France, together strongly supported the notion of a natural pro-
gressionalongtheAtlanticcoastfromtheMediterranean. AsToonenotesinhisreviewof
thistopic(2005),bytheendof1863Borrer,BabingtonandBoswell-Symehadallagreed
thatthecaseforitbeinganativespecieswasstrong. Mansell-Pleydell(1874)addedhim-
self to this list in his ‘Flora of Dorset’. H. C. Watson provided the only opposition, sug-
gesting the possibility of an association with planted trees or shrubs. Townsend (1904)
reported the idea that it could have been introduced, along with other species, with the
imports, around 1800, of young fir trees to Bournemouth from the Landes area of France
(where a similar G. illyricus was known to grow). However, evidence does not support
anycorrelationbetweenthegrowingareasofthesetwospecies. Assuch,Ithinkitisrea-
sonable to assume that the first records were not an account of a spreading introduction,
butrathertheinitialdocumentationofanestablishedpopulation.
A picture emerges that suggests a lower bound on the age of the Britain plants is of
the order of many hundreds of years. It could be considered even higher, depending on
the rating of the likelihood of jump dispersal events. Assuming that the Isle of Wight
population was once a part of a mainland range puts the lower bound at being over 7000
yearsago(CooperandJay,2002). Rejectinglongrangedispersalaltogetherandtherefore
assuming that G. illyricus arrived in Britain by migration, fixes the arrival time to before
thelastformationoftheChannel,about8000yearsago.
Theupperboundisalittlemorecertain,beingdefinedbythetimetablefortheincrease
in temperatures since the last glacial maximum, over which the ice sheet and permafrost
retreated north allowing plants growing in the refugia along the Mediterranean to rapidly
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2.Background G.illyricusinBritain
spread north and recolonize Europe (Hewitt, 1999). Temperatures started to rise again
from about at least 18,000 years ago (the lower bound for the last glacial maximum or
LGM), at which point southern Britain, connected to France at the time, was within the
limits of the permafrost and mostly covered by the ice sheet of northern Europe (Taber-
let etal. 1998). After a period of warming, the Younger Dryas stadial (Berger, 1990)
meant Britain still had sub-zero mean annual temperatures until about 11,500 years ago
(Atkinson etal. 1987). This ended abruptly when temperatures rose by as much as 7◦C
in a matter of decades and then steadily increased to near present averages (Alley, 2000).
The climate of the south coast of England permanently reached temperatures suitable for
G. illyricus maybe as soon as 1000 years later. Migration is an additional limiting factor:
after the LGM, the maximum migration rates achieved were an impressive, but bounding,
2km per year (Bennett etal. 1986). It seems, therefore, that G. illyricus was probably
notgrowingintheprecursoroftheBritishIslesmuchbefore10,000beforepresent. How
long after this G. illyricus could have actually arrived would be nothing more than guess
atthispoint.
Today, there is a definite trend of decline (Brewis etal. 1996). For example, a search
in1947concludedthatitgoneextinctontheIsleofWightsincethelastsightingin1931.
Within the New Forest itself, the smaller sub-populations are slowly disappearing. The
matter might be all the more pressing for the fact that its decline is also being seen in
France. Sub-populations are known to have gone extinct, including the crucial Belle Isle
(Brittany) population, which is thought to be the most closely related continental popu-
lation to the British plants (Stokes, 1999). Like across the whole of North West Europe,
a huge percentage of France’s heathland has been lost over the last 200 years (mainly to
agriculture) and this is undoubtedly a significant factor. A trip to France undertaken to
collectsamplesforthisprojectatknown,albeitalmosthistoric,locations(Abbayesetal.;
Boreau, 1857; Coste, 1906; Lloyd, 1844; Lloyd, 1886; Souche´, 1901) found that in most
places, areas of suitable habitat were nowhere to be seen. The most promising locations
were on rocky, heathered slopes above the River Argenton between Argenton-Chaˆteau
and Thouars, but no sign of any Gladiolus were found. This author would not be sur-
prised to discover that G. illyricus is extinct in the Loire Valley. Hence the importance
of determining the resources and effort that should be spent on the conservation of the
specieshereinBritainnow.
7
3.MaterialsandMethods G.illyricusinBritain
numberofspecimens
12
successfullysequenced(total = 49)
failedtosequence(total = 17)
5
4
3
2
1
0
75431097654320965421098643207080
00000099999999888888877777776655 year
00000099999999999999999999999999
22222211111111111111111111111111
Figure3: Successinthesequencingoftheherbariumspecimens,influencingwhichwereselected
for processing. Keeping track of sequencing successes meant that it could be safely guessed
that the last six oldest samples were unlikely to succeed and effort was spared by not attempting
extractions.
3 Materials and Methods
Leafsampleswereobtainedfromtwosources. Firstly,alicensedfieldtriptotheNewFor-
estattheendofthefourthweekinJuneprovided52smallleafsamples,eachstoredsep-
aratelyandimmediatelyinsilicafilledbags. AllNewForestspecimenswereidentifiedas
G.illyricus. LocationsarelistedinAppendixA.
Secondly, samples of G. illyricus, G. communis, G. italicus, G. atroviolaceus, G. tri-
phyllos, G. anatolicus, G. imbricatus and G. palustris, collected from around the Medi-
terranean over the last fifty years, were taken from specimen sheets in the herbarium at
the University of Reading. Full details are listed in Appendix B. Selection was mainly
dictated by availability. Specimens collected more than fifty years ago were omitted due
to the poor outlook on DNA sequencing success, although specimens that might poten-
tially have become key to uncovering relationships were kept. Sheets that were overtly
of poor quality or paucity were also overlooked. Sixty two sheets remained from which
0.5–3cm2 ofleafmaterialwastaken.
Carewasalsotakentoensurethattheoriginaldeterminationwasplausible. Sixspeci-
menswereconsideredincorrectandelevenwerepossiblyincorrect(notesaregivenalong-
side the relevant entries in the appendices). Tutin etal. (1980) was mostly used for the
keys,withthecomplicationthatonlyasubsetofthecharacterscouldbeused,becausethe
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3.MaterialsandMethods G.illyricusinBritain
plants were dried herbarium specimens. Many of the taxonomically informative distinc-
tions between these species are in the morphology of the flowers, including the perianth.
Thoseusedfordifferentiationwereasfollows. BetweenG.illyricusandG.communis:
plantheight leaflength leafwidth no. flowers
G.illyricus 25–50cm 10–40cm 4–10mm 3–10
G.communis 50–100cm 30–70cm 5–22mm 10–20
i.e. whether the specimen was large or small. The distinction between G. communis
ssp. communis and ssp. byzantinus was not made, because over the limited range and
quality of specimens available, a consistent separation was not observed. The principal
difference used for the differentiation of G. italicus from G. communis (both having a
highly overlapping range of values for the above size characters) was the anther-filament
lengthratio:
G.communis anthershorterthanfilament
G.italicus antherlongerthanfilament
Ambiguityarosewhentheywerethesamelength,althoughexactmeasurementswerenot
takenbecausetheofthefragilityoftheherbariumspecimensandtheinvasivenessofsuch
measuring. TheoneG.palustrisspecimenwasveryhardtodistinguishfromG.illyricus.
Differences between the other species encountered were more definitive. Key characters
usedinclude:
species mostdistinctcharacter notes
G.atroviolaceus flowersdeepviolet-purple wellpreservedonherb.sheets
G.anatolicus seedsunwinged fromnoteonherbariumsheet
G.imbricatus denseflowerspike butfewflowers
G.triphyllos leafwidth<5mm noticeably“straggly”
The last species, G. triphyllos, is endemic to Cyprus and so was keyed out using Meikle
(1985).
PrimerSelectionandSequencing
To ensure success of the field collecting, the New Forest trip had to wait until it was
certain that any potentially flowering plants were actually in flower. The knock-on effect
was to delay the laboratory work. As such, reliable markers were chosen for sequencing
targets. Reliableinthiscontextmeanshighcopy,monomorphicgenomeregionsofwhich
9