~peciation
an d Radiation of the Espeletiinae in the
An des JOS E CUA TRE CAS AS
CHAR ACTE RfZA TfOf\ J OF THE ESPE LETII NAE
The Espe letiin ae (A stera ceae . tribe Helia nthea e) comp rise a group of abou t 130 species of highly e volve d fto\ve ring plant s. They are geographically and ecolo gical ly highly speci alized to th e pecul iar life cond itions of the north ern sectio n of the tro. pic:.ll Ande s. Deta iled chara cteriz ation s are available in the origin al descr iption of the subtr ibe (Cuat recas as, 1976) , and in the autho r's n1onograph . \vhich is in final prepa ratio n. At this time it may suffice to point ou·t the mo{.)t" outstan~ing differ ential featu res. of the subtr ibe Esperetiiriae \Vithin· the· · Heliantfle ~i-e··: ( T) spira l · phyllotaxis~ · (2) obpy ran1idal shape of the .ache nes, \vhich are , in addit ion , smoo th, \vitho ut striat ions, glabr ous . and epap-pose (with a n1inin1al excep tion); (3) xerom orphi c structu~e and organ izatio n of the bioty pes, inclu ding head s and leaves; (4) fertile fernale rav. flowers and functionally male disc fto\ve rs; (5) basic chro n1oso rne nurnb er /\' = 19. Thes e chara cters separ ate the Espel etiin ae from other group s of the tribe such as tvfelan1podiinae and Polvm niina e, as descr ibed in other \vork s (Ben tha1n , 1873; Hoff mann _, 1890-1894~ S.tuessy, 1973 , 1977; Robi nson , 1981). ~
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basis. (_)ther impo rtant taxo nomi c fcciturcs are found in the inflor escen ces and gro\vth forms. Some bf these struc tural \·aria tions undo ubted ly repre sent evolu tiona ry trend s that are influe nced by the extre me envir ontne ntal facto rs prevailing in the north . . ern tropic al Ande s . Thre e n1orphoiogical featu res seem most signif icant in the differentia tion and e\ft®lution of the Espel etiina e: leave s, inflor escen ces, and biotypes. '-
·Leaves
The leave s are usually large . up to 50 X L2 (70 x 25) em, the blade s vario usly oblon g. elliptic to linea r, only slightly atten uate at the base, there fore se ssile~ or atten uate and proxirnally contracte d into a tnore or less distin ct petio le. The tnargin is revol ute. entire or minu tely retno te tooth ed; the venat ion is pinn a te ~ usually pron1inent with a robus t midd le nerve . The sheat hs are usually e nlarged~ ampl ectan t or semia tnple ctant to the stem. mostl v- imbri cated on iC they. are eithe r open and flat, or curvj ng only to embr ace the stem with free marg ins. or encircling the stem and tubul ar. The bl ades mav be . mode rately -trtibesc-enror m-ore·usTJally·a·e nse1Y'iesfe·a ;·-a:rTec.ist on the lo\ve r side , the vestu re is frequ ently very thick , the blade s Janate or seric eous. The sheat hs are usually serice ous on the abaxi al side. Th~ great range of varia tion indic ated in the shape and size of the blade s. venat ion, and qual- · ity and densi ty of indun 1entu m is impo rtant \vhen consi derin g speci ation . The struc tiJre of the lea f base has in1po rtanc e at the gener ic level ; e.g., tubul ar sheat hs chara cteriz e L ibano rha1nnus and Carranzbo a, open sheat hs the other gener a (Fig. ll-1) . Impo rtant trend s of evol~tion in the Espel etijnae are on one hand the trend that has. favor ed the tubul ar type of sheat hs an q, on the other , a -
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CHAR ACTE RIZA TION OF INFR A SUBT RIBA L TAXA
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Varia tions in nurnber:- shape , size. color . and kind or densi ty of tricho rnes for every given part provi de floral or veget ative chara cteris tics of taxonon1ic value at the sp~.cific ]eve] and to some gener ic level. Varia tions in leaf oute :-o-~n t at the ..... line and type of indum entum are basic consi deration s for specit!c distin ction s. Some aspec ts of th e leaf struc ture and archi tectu re are impo rtant in gen eric differentiation , and phylo genet ic trend s in the Espe letiin ae may be traced on that
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