Maguire, Bassett & Wurdack, John J. 1961. The botany of the Guayana Highland--part IV (2). Mem. New York Bot. Gard. 10: 1-87.
Melastomataceae
Latin Diagnosis - M. subumbellatae Tr. affinis sed cum foliis cordatis et thecis antherarum minus valde dorsaliter curvatis. Subg. Pericrene sect. Gyrtotheca. Frutex glaber 1-3 m altus. Folia sessilia crasse coriacea (3.5-)6-10 X (2-)3-6 cm ovata vel oblongo-ovata apice per ca. 5 mm subabrupte acuminata basi rotundata et leviter (2-3 mm) cordata vena centrali supra insculpta subtus vix elevata nervis lateralibus non vel vix evolutis supra et subtus anguste obscureque insculptis. Inflorescentiae in foliorum superiorum axillis 1-3-aggregatae singulae 1-3-florae; pedunculi 3-15 mm longi; pedicelli 3-12 mm longi circa medium bibracteolati; bracteae bracteolaeque 3-6 X 1-2-2 mm lanceolatae ascendentes post anthesim plus minusve persistentes. Flores 5-meri. Hypanthium (usque ad torum) 3.2-3.5 mm altum; calycis tubus 0.7-1 mm altus, lobis 1.3-1.5 X 3-3.2 mm depresso-triangularibus ad margines vix flmbriato-ciliolatis singulis extus minute unidentatis mucrone ca. 0.2-0.3 mm eminenti. Petala 9.5-9.8 X 6-6.5 mm oblongo-ovata apice attenuato-acuta undique dense granulosa. Filamenta 7.5-8 mm longa; antherarum thecae 2.3-2.7 mm longae uncinatae dorsaliter vix prolongatae, glandula dorsali 1.5-1.7 mm longa, connectivo sub thecas usque ad filamenti insertionem ca. 0.3 mm prolongato postice in calcar 1.1-1.4 mm longum hebeti-acutum protracto. Stylus 13-14 X 0.6-0.75 mm; stigma punctiforme 0.3 mm diam.; ovarium 5-loculare in cuique loculo 4-ovulatum placenta basilari. Fructus i.s. depresso-globosus ca. 10 mm diam. 3-5-spermus; semina ca. 6 X 4 mm asymmetrice ellipsoidea nitida laevia.
Anatomical features: margins of midrib xylem turned up, in, and slightly down at the very edges, not touching each other nor the upper surface of the xylem; foliar stone cells above and below the midrib xylem extending less than one-fourth the distance from the node to the midrib tip; foliar terminal sclereids filiform, running vertically between the epiderms and there turning and spreading out horizontally as Avell as usually branching; stomatal crypts simple, 75-110 per square m m , the cavity averaging ca. 31 µ in diameter and 120 µ deep, the mouth ca. 5 µ in diameter; upper epidermis double, the outer layer with more cells than the inner, the lower epidermis single, the inner walls of the lower epidermal cells and of the cells of the inner layer of the upper epidermis from frequently to not at all mucilage-thickened; hypodermis absent except near the midrib; floral terminal sclereids short-filiform, occasional in calyx lobes, rare in petals, otherwise absent; floral stone cells absent. Within the sect. Gyrtotheca, M . uncitheca shows the following unusual features:
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 relatives.
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 unknown.
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 phylogenetic 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-mse particularly 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 connective. In M . subiunbellata 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 . densifoliata, 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.