Pentamerista neotropica Maguire

Authority

Maguire, Bassett. 1972. The botany of the Guayana Highland--part IX. Mem. New York Bot. Gard. 23: 1-832.

Family

Tetrameristaceae

Scientific Name

Pentamerista neotropica Maguire

Discussion

Wood.

The wood specimen studied represents a small tree having an outside diameter of 4 cm. The bark is about 50 mm thick, reddish-brown obscured by a gray lichen coating, and furrowed longitudinally in irregular plates. The bark structure in cross section shows closely set patches of light gray stone cells that are roughly circular in outline and are aggregated axially into long crystal-like masses. No ray flares are evident in the secondary phloem. The secondary xylem is diffuse porous, about 3 cm diameter and nearly circular in section. The wood is light brown in color with no sap-heartwood differentiation. Pores and rays small, visible only with a hand lens. Ray fleck low and dark. Parenchyma visible with hand lens as fine, interrupted tangential bands. No odor or taste. Texture fine and uniform, but distinctly closer near the pith. Ripple marks and gum ducts lacking.

1. Vessels. Pores in the outer xylem mostly in pairs radially grouped with a few solitaries, and some multiples up to four. The pores in these multiples are appressed with flattened contact faces and slightly necked between cells; tangential diameters average 100 µm (range 75 to 120 µm). The pore multiples average about 9-10 per mm2. For the xylem near the pith the pore groups are mostly in threes with a few up to six, the tangential diameters decrease to an average of 75 µm, and the density of the pore multiples increases to 12 per mm2.

Vessel elements are medium length averaging 0.76 mm (s = 0.110 mm, sx = 0.011 mm, Cv = 14.5%). Perforations mostly simple, with about 8 percent of the small-diameter elements exhibiting scalariform perforations of 3 to 6 slender bars (evident only in preparations of macerated cells). The ends of vessel elements are oblique, slanted 40 to 60° with element axis, and exhibit some short tails. Vessel walls are thin, averaging 2 to 3 µm.

Tyloses not evident. Reddish-yellow gum plugs common. No helical thickenings.

Intervessel pitting alternate, minute (3-4 µm diameter), crowded but not sharply angled. Pit apertures slit-like, horizontal, included.

Ray-vessel pitting in central portion of ray similar to intervessel pitting but smaller (about 2 µm diameter) and not so crowded with apertures that are less elongate. In the marginal part of the rays the pitting of the upright cells is somewhat more simple and has a tendency to coalesce into elongated forms.

2. Axial parenchyma. Apotracheal, diffuse to diffuse-in-aggregates with tendency toward uniseriate tangential bands. Strands average 5-6 cells with a maximum of 12. Individual cells average 30-32 µm tangential diameter, 200 µm in length, and have a wall thickness of 1.5 µm. Pitting is simple, minute, and sparse. Strands are not crystalliferous.

3. Rays. Rays heterocellular (Kribs Type I), almost no uniseriates evident on tangential section, but clearly two-sized on the cross section because of the long narrow marginal portions; closely spaced, average 6 per mm; not storied.

The widest part of the rays is the central portion that is medium width (70 µm) and usually triseriate with about 20 percent of rays biseriate. The height of this central portion is 12 to 13 cells and about 0.60 mm in the axial direction. The central parts of the rays consist of cells which are rounded to oval-elongate in tangential section; in radial view most of these are not radially elongate as in the usual procumbent ray cells but are square to rectangular with the smaller dimension in the radial direction. These cells have some resemblance to tile cells but are not so narrow in the axial direction nor as uniform in size. Walls of these “procumbent” cells are about 3 µm thick and markedly simple pitted with a tendency to anastomosing pit canals. A part of these “procumbent” cells are slightly enlarged and contain bundles of raphides enclosed in a more or less evident gelatinous envelope. These raphides may be oriented radially, axially, or diagonally to the ray axis.

The margins of the rays consist of uniseriate tails of quite variable height and often not equal above and below. These margins average 6 cells or 0.48 mm tall, with a range from 1 to 12 cells and 0.1 to 0.48 mm. The uniseriate tails in the radial view consist of upright cells with the axial dimension about twice as great as the radial dimension (45 × 95 µm). The walls about similar to those in the “procumbent” cells. No crystalliferous cells (raphides) present.

4. Fibers. Fibers medium to long with an average of 1.71 mm (s = 0.254 mm, sx =0.0248 mm, Cv = 14.9%). Fiber diameters average 28 µm tangentially. Fiber walls 9-10 µm thick. Pitting distinctly bordered with pit chambers about 3 µm diameter, and inner pit apertures flattened and slightly extended. Pitting more common on radial faces than on tangential by a ratio of 2.5 to 1. Fibers non-septate.

Material studied. Collected on the Yapacana Savannas, Alto Rio Orinoco, Territorio Amazonas, Venezuela, 16 Sep 1957, Bassett A. Maguire, John J. Wurdack & Wm. M. Keith, Jr. 41486.

Summary of Wood Characterizations.

The samples of Pentamerista neotropica Maguire and Tetramerista glabra Miq. that have been examined exhibit certain similarities in their xylem tissue:

1. Bundles of raphides are present in the central portion (procumbent cells) of the rays and are absent in the marginal upright cells of the rays.

2. Rays are heterocellular, Kribs Type I essentially, with the marginal portion of upright cells higher in the axial direction than the central, multiseriate portion of the ray.

3. Axial parenchyma apotracheal diffuse to diffuse-in-aggregates.

4. Vessel elements are longer than average for xylem of dicotyledons.

5. Intervessel pitting alternate, minute, closely spaced but not angled through crowding to any extent.

6. Ray-vessel pitting similar to intervessel pitting essentially.

The samples of the two genera differ:

1. The central portion of the xylem rays in Tetramerista glabra Miq. is composed either of the usual, radially elongated procumbent cells or in other samples, of cells that are square. The central portion of the rays in Pentamerista neotropica Maguire consists of cells that are nearly square in radial view or longer axially than radially with an overall appearance that approaches that of tile cells.

2. The raphide bundles in Tetramerista glabra Miq. occur in enlarged procumbent cells and are radially aligned. In Pentamerista neotropica Maguire the raphide-bearing cells in the central part of the ray are hardly any different in size and the long crystal axis may be oriented at any angle with the stem axis.

3. Perforation plates are entirely simple in Tetramerista glabra Miq., but in macerated preparations of Pentamerista neotropica Maguire it is evident that about 10 percent of the vessel elements are scalariform with 3 to 6 slender bars.

Leaves. Leaves are exstipulate, simple, entire, chartaceous or coriaceous, oblanceolate, narrowed to a subsessile base or very short petiole. Nervation is pinnate, prominent on the upper surface (when dry), and prominulous on the undersurface in Tetramerista or obscure in the more coriaceous leaves of Pentamerista.

Leaf base. In Pentamerista cross sections of petiole reveal a 3-4 small lateral vein supply to the winged base of the lamina. The central or costal petiolar vascular bundle is elliptic-cylindric or annular, revealing the normally oriented and succession of tissues (Fig 33). Raphide crystal-containing idioblasts are commonly found in the parenchyma.

Sections at the midportion of the midrib (Fig 34) show a most interesting twinning of the vascular element to have taken place, forming dorsi-ventrally superposed vascular strands, each with the usual complement and sequences of tissues, but now both oriented normally with the xylem elements ventrally positioned and the phloem elements dorsally positioned. Bundle sheath elements are densely filled with a substance darkly staining with Saffranin O.

The upper epidermis (Fig 35) consists of isodiametric pentagonal cells ca 30 µ diam, with fairly thick outer walls. The lower epidermis consists of somewhat smaller cells ca 15 µ diam, and is provided with a single layer of hypoderm (adaxial in Tetramerista) cells of slightly larger size. Stomata have a density of about 190 per sq mm. The stomatal opening is 25-30 µ lengthwise. Stomata are confined to the lower surface, are ranunculaceous, commonly with five slightly depressed bordering cells. The guard cells are provided with conspicuous double cuticular ledges, one inner and one outer (Fig 36).

Metcalfe & Chalk (p 399, 1950) report a hypodermis of pitted cells below the upper epidermis for Tetramerista [glabra]. No such hypoderm has been detected for Pentamerista. The palisade mesophyll consists of 2-3 rows, Raphide-bearing cells are especially common among the palisade cells—less so in the spongy mesophyll.

Inflorescence. The inflorescence is indeterminate, hence subcorymbosely racemose. Peduncles are axillary, solitary, somewhat angled, 6-10 cm long; pedicels 12-22 mm long, distal, subcorymbosely arranged, each subtended by a pair of bracteoles 2-3 mm long. Bracteoles early deciduous in Pentamerista, persistent in Tetramerista.

Flowers. The calyx consists of 5 quincuncially arranged (Fig 37) soon deciduous, oblong sepals in Pentamerista. In Tetramerista the sepals are 4 and are persistent, presumably the fifth of the original five having been lost, hence the outer pair and numbers 3 and 4 of the inner series remaining. The same sequence obtains for the petals, being fundamentally quincuncial in primitive Pentamerista and reductively four in Tetramerista, with the loss of presumably the associated fifth petal, the associated fifth stamen, and the associated fifth carpel, resulting in the complete tetrameristicity of Tetramerista. It is thus assumed that Pentamerista of the New World is the primitive or deriving genus, and Tetramerista of Malaysia is the derived genus. This fits with differences in wood structure.

In both genera the sepals are characterized by having conspicuous, ventrally medianly located, deep-seated flask-shaped glands which appear as pores or slits on the inner surface (Fig 38). Interestingly, deep-seated glands of the same character (Fig 38) are to be found occupying also the median inner center, and there only, also of the sepals of Pelliciera, the unitypic genus giving rise to the related Pellicieraceae (Melchior, 1964, Beauvisage, 1920, and Hutchinson, 1959). Raphides are found in most tissues of the Tetrameristaceae and also apparently in the Pellicieraceae.

Stamens are 4-locular and introrse, 5 in Pentamerista, 4 in Tetramerista. Raphides are common especially in the connectives of the first, and presumably in both genera (Fig 39). Dehiscence is accomplished lengthwise by the rupturing of a line of weak wall cells (Fig 40G).

The pollens of Pentamerista and Tetramerista are similar. The characterizations of pollen here offered in the description of the family and in the description of Pentamerista neotropica were drawn from observation of both water mounted and acetolized pollen grains observed under the light microscope, and gold-coated grains observed under vacuum by means of the Hitachi Scanning Electron Microscope, Model SSM-2. The water mounted and the vacuum treated grains, in this instance, more nearly retained presumably original form and dimensions. Acetolized pollen, again in this instance, evidently suffered the greatest distortion, especially by elongation along the polar axes.

The remarkable differences in size and form produced by the several techniques would seem to present difficulties, at least sometimes, in correlating measurements and descriptions as they have been recorded in the literature, and as they may derive from the several palynological techniques now available in contemporary study.

The ovary is 5-locular in Pentamerista, or 4-locular in Tetramerista, the ovule solitary, bitegumentous, anatropous, basifixed in each locule. Endosperm is copious, enveloping the erect embryo.

The style is subulate with a small distal crateriform stigma.

Fruit baccate, 5- or 4-seeded. The seed are conspicuously different from those in all other families in the Theales, being large with a thick multicelled seed coat of essentially rectangular or pentagonal stone cells provided with numerous bordered pits (Fig 40A, 44C, D). The endosperm is voluminous, encasing the erect basal dicotyledonous embryo in which cotyledons are about one-fifth the length of the embryo (Fig 40A-C).

Phylogeny—Relationships.

In the Theales the prevailingly fundamental flower organization provides for a quincuncial arrangement of the perianth members, with the 5-merous arrangement in the androecium and gynoecium. A complete 5-merous flower organization, therefore, is presumed to be primitive in the Theales, and departure therefrom to be advanced.

In Pentamerista we find the presumptively more primitive completely 5-merous condition. Tetramerista with 4-merous flowers is considered to be derived. In any consideration of the place of origin of the family, one is required to assume the area of the New World tropics, more especially Guayana, as the place of origin, with the establishment of and differentiation of Tetramerista in Malaysia resulting from early migration from the ancestral home in Guayana, or from a common progenitor.

Economics.

New World Pentamerista is not known by us to have any economic uses. Tetramerista of Malaysia, common name Punah, becomes a medium-sized tree reputedly reaching a height of 30 m and a diameter of some 3 ft. Desch (1941) describes its general and mechanical properties, and comments on its importance and uses as follows: “Importance and uses.—Although the species is limited in distribution, punah is an important timber species in certain of the coastal swamp-forests, and the erection of saw mills in these localities is making the timber more widely known. It is said to have been commonly obtainable in the Singapore market, log supplies coming from the adjacent Dutch islands, and to have been used for constructional work not in contact with the ground. Pine-apple factories do not like punah for boxes because of its liability to splitting when nailed, but it has adequate strength properties for house building and should prove an economical building timber for interior use.”