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Angiosperm Classification

Describe major past – present classes of flowering plants (Linnaeus,

Cronquest, Dahlgren, APG 1!!, "te#ens $%%1 onwar&s' )here these

classifications inten&e& to reflect ph*logen* an& how successful are the* in

this regar&+ s this finalise&+

Characteristics of Angiosperms are-

• .essels in the /*lem

• "ei#e elements an& companion cells in the phloem

• 0he embr*o sac of eight nuclei (one egg, two s*nergi&s, three

antipo&al an& two polar'

• Double fertilisation

•

Close& carpels0here are numerous e2ceptions to the abo#e charateristics in Angiosperms

Ph*logenetic classification is the ultimate aim of ta2onom*

Lamarck  – "uggests that the characters use& for formal classification &i&

not nee& to be use& for i&entification 3emember 4ren&on this bloe was a

&ichea& an& not to be truste&5

6or interest sae, people lie Asa Gra*, 4entham an& 7ooer trie& to

classif* all nown plants into fi2e& numbers of ta2a for memor* sae eg4entham an& 7ooer propose& that the best si8e for ta2a was $9: members,

*et some of the families the* accepte& ha& up to a hun&re& members (0a2a

might be &istinct but rans are not fun&amentall* &ifferent'Dichea&s5

Linnaeus – focuse& on genera for ta2anomic classification an& belie#e& that

in&i#i&ual genera an& species e2iste& in nature, whereas large groupings

were for human con#enience 6eatures of the flower an& fruit shoul& be use&

to &istinguish genera an& #egetati#e features to &istinguish species 7e also

 propose& that ;genera e2ists in nature in&epen&entl* of the features use& tocharacterise them<, therefor he &i& not change generic &escriptions before

a&&ing new species to them Dichea&5

Engler system – =ngler classifie& plants accor&ing to the primiti#eness of

their features 0herefore Amentiferae (4utalaceae, >uglan&aceae an&

6agacaea' were place& before ?agnoliaceae because it was consi&ere& more

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 primiti#e 0his is not the case an& the famil* Amentifereae is now

consi&ere& to be an a&#ance& heterogenous group an& not monoph*letic

=ngler also place& monocots before &icots, a position which has been

re#erse& recentl* =ngler faile& to recognise the significance of re&uction

an& therefor thought that simple meant primiti#e

Cronquist in 1!1 classifies Angiosperms at &i#isional ran an& treats

&icot*le&ons an& monocot*le&ons as classes that in turn are broen into

subclasses Cronquist &oes not use the categor* of super9or&er "*stem has

fi#e subclasses of monocot an& si2 classes of &icot, unlie three an& se#en

 b* 0ahtajan Cronquist inclu&es 0ahtajan subclass 3anunculi&ae with

subclass magnolii&ae to account for the &iscrepenc* in &icot subclasses, an&

similarl* seperates subclasses Commelini&ae an& 8ingiberi&ae from

0ahtajan huge subclass Lilii&ae

Dahlgren &e#elope& an informati#e classification of Angiosperms base&

upon the &istribution of a wi&e range of phenetic characters ?an* consi&er

this to be the best classification &e#elope& n his classification Angiosperms

are equi#alent to the main groups of G*mnosperms 0he Angiosperms are

&i#i&e& into two subclasses – &icots an& monocots or ?agnolii&ae an&

Lilii&ae respecti#el* 0his gi#es the subclasses broa&er circumscription than

the pre#ios classes of Cronquist an& 0ahtajan t is note& that the &i#ision

 between &icots an& monocots woul& not be allowe& following rigi&

classification but belie#es monocots are a unique group worth* of cubclass

ran Dahlgren allows further sub&i#ision of subclasses into superor&ers

 bearing the termination –iflorae, which allows increase& fle2ibilit* in

in&icating affinities which ma* otherwise b* the subclasses of Cronquist an&

0ahtajans