Arthrostylidium cacuminis McClure
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Authority
Maguire, Bassett & Wurdack, John J. 1964. The botany of the Guayana Highland--Part V. Mem. New York Bot. Gard. 10: 1-278.
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Family
Poaceae
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Scientific Name
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Description
Latin Diagnosis - Culmi humiles, vix 60-centimetrales et 2 mm diametro (vel pro parte basali tantum 2 cm longa suppetente 3 mm diametro) omnino glabri, internodiis inanibus usque ad 45 mm longis cylindratis, nodis supra eicatricem mediocrem inflatis; culmi vaginae desideratae; rami (in specimine) solitarii omnino glabri, nonnullis ad basim bulbosis, vaginis desideratis; foliorum vaginae paucae vel plures (usque ad 12) supra medium nervoso-striatae carinataeque, in dorsum marginesque glabrae, ad apicem utrinque productae, auriculis obsoletis, setis oralibus nullis vel paucissimis, usque ad 2 mm longis, pallidis, glabris, ligula interior 2-3 mm longa, ad apicem truncata vel paululum rotundata, ad marginem Integra vel minute erosa, in dorsum glabra, ligula exterior lineola, ad marginem integra, in dorsum glabra; foliorum laminae usque ad 16 cm longae et usque ad 2 cm latae, lanceolatae vel oblongo-lanceolatae, in apicem acutum attenuatae, basi in petiolum fuscum glabrumque rotundatae, dempta pagina inferiore minute papillosae paginis utrisque marginibusque omnino glabrae, costa subtus tantum basin versus invalide manifesta, nervis secundariis tertiariisque invalidis, venulis transversis non manifestis. Inflorescentia vel axillaris vel ramos foliiferos terminans, subspicatoracemosa, pedunculo vix exserto, rhachi usque ad 27.5 cm longa, gracili, omnino glabra, tereti, supra insertionem pedicellorum sulcata, bracteis pedicellos subtendentibus obsoletis, pedicellis 5-25 mm distantibus, millimetralibus, semicylindratis, adpressis, apice bicarinatis, omnino glabris; spiculae adpressae, juveniles teretes, arctae, usque ad 20 mm longae, 3-4-florae, maturitate compressiuseulae mox diffractae, floscula suprema ad lemma sterilem valide involutum subsetiforme reducta, rachillae segmentis compresso-clavatis, apice subito paululum dilatatis, omnino glabris nitidisque, inferioribus infra medium superioribus supra medium paleae attingentibus, infra lemma et supra glumam vacuam superiorem disarticulantibus, giumis vacuis vulgo 2, approximatis, pallide stramineis, papyraceis, submembranaceis, fragilibus, subaequalibus 5-6 mm longis, extrinsecus omnino glabris, intus apicem versus albo-strigosis, dorso carinatis, apice submucronatis; lemma usque ad 9 mm longum, viridi-stramineum, paulum indurate papyraceum, fragile, apicem versus obtusum carinatum, alibi nervibus plerisque submersis plurinerve, dorso marginibusque glabrum intus apicem versus minute et antrorse albo-strigosum; palea lemma aequans vel plus minusve valde superans, papyracea, marginibus hyalina, apice obtusa, sulco glabra vel sursum leviter hispidula, extra carinas glabra invalide paucinerviisque, carinis glabra vel subglabra; lodiculae nuUae; antherae non inventae; ovarium fuscum glabrum; stylus solitarius apice divisus in stigmatibus 2 brevibus invalide ramosis vel hyalinis. Fructus maturus desideratus.
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Discussion
Type. Occasional in dense elfin forest, vicinity of Summit Camp, alt. 1500 m, Cerro Huachamacari, Rio Cunucunuma, 15 Dec 1950, Amazonas, Venezuela, Bassett Maguire, R. S. Cowan & John J. Wurdack 30249 (holotype US, isotype NY).
In superficial floral characters this species closely resembles A. scandens MeClure, from which it differs in the almost complete glabrousness of the vegetative and reproductive parts (at least those present in the type specimen), in the flared apex of the rachilla-segments, in the absence of lodicules, in the shape of the apex of the leaf-sheath, in the weaker development of the oral setae of the leaf-sheath, and in the narrower leaf-blades. The absence of lodicules is correlated with an absence of evidence that the florets open at anthesis, and with the hyaline form of the stigma in an occasional floret.