1961] 



BOTANY OF THE GUAYANA HIGHLANDS PART IV (2) 



47 



the midrib ; floral terminal sclereids short-filiform, occasional in calyx lobes, rare 

 in petals, otherwise absent ; floral stone cells absent. 



Within the sect. Cyrtotheca f M. uncithcca shows the following unusual fea- 

 tures : 



1. The moderately inrolled midrib xylem, in which the margins are rolled 

 up and in but scarcely turn down at all, as compared to the other species in 

 which the margins turn down so as almost to touch the upper surface of the 

 xylem. 



2. The thick, ovate-cordate leaves, as contrasted with the slightly thinner 

 elliptic leaf blades with abruptly acuminate bases of the near relative^. 



3. The large bracts, which exceed in size those of other members of the 

 section with the possible exception of M. subumbellata, whose bracts are un- 

 known. 



4. The relatively long anther gland and very short dorsal prolongation of 

 the anther sacs, with the near relatives having more nearly equal distribution of 

 the thecae on both sides of the connective. 



M. uncitheca is clearly the least specialized member of the section, judging 

 by the two characters that almost certainly have pli ylogenetic significance : the 

 form of the midrib xylem and the form of the anther. The former feature, as 

 described above, appears definitely to be less complex in our new species than 

 in the other members of the section. The anther form is evolution-wise partic- 

 ularly illuminating; it illustrates the first step in the phylogenetic movement 

 of the pollen sacs from the usual ventral position to the gland side of the con- 

 nective. In M. subumbellata and in some specimens of M. densifoliata Ducke the 

 pollen sacs lie about one-third on the gland side of the anther and two-thirds on 

 the opposite side ; in other specimens of M. densifoJi<it<i, in M. dumetosa Cogn., 

 and in M. crassifolia Sagot, the pollen sacs are about equally distributed on 

 both sides; and in M. anomala Pulle, more than one-half of the thecae is on the 

 gland side. Thus M. uncitheca seems most closely related to M. subumbellata 

 on the basis of anther morphology. Other characters, however, are inconclusive, 

 and, in view of the differences listed above, the new species cannot be said to 

 have a truly close relationship to any of the other section members. 



ACANTHACEAE 4 



Chaetochlamys wurdackii Leonard, sp. nov. Fig. 34. 



Herba usque ad 50 cm altam, caulibus basi 4.4 mm crassa, subquadrangulari- 

 bus, bifariam hirtellis vel basi glabris, pilis recurvatis usque ad 0.3 mm longis, 

 cystolithis pluribus, 0.064-0.112 mm longis, parallelis ; lamina foliorum inferiorum 

 oblongo-ovata, usque ad 10 cm longam et 3 cm latam, acuta vel subacuminata, 

 basi acuta, petiolata (petioli graciles, 1-2.5 cm longi, puberuli, pilis curvatis, 

 circa 0.1 mm longis), supra (sicca) prasina, parce pilosa et ciliata, pilis paten- 

 tibus, usque ad 1.5 mm longos, subtus olivacea, glabra vel costa parce et minute 

 puberula, costa et venis lateralibus (6-8 paribus) subtus aliquanto prominen- 

 tibus, supra obscuris, cystolithis aliquanto obscuris, usque ad 0.32 mm longos, 

 gracilibus; folia 4 apicalia inflorescentiam subtendentia ovata, usque ad 11 cm 

 longa et 5 cm lata, breviter acuminata (apice ipso acuto), basi rotundata, sub- 



4 By Emery C. Leonard. Published by permission of the Secretary of the Smithsonian 

 Institution. 



