Изображения страниц
PDF
EPUB

A NATURAL GROUP OF UNUSUAL BLACK OAKS.

(PLATES II TO IV.)

BY WILLIAM TRELEASE.

(Read April 21, 1921.)

Though most oaks bear only one or two acorns in a leaf axil, it is recognized generally that even when essentially sessile these fruits and the flowers that produce them really pertain to a reduced pistillate catkin which is comparable with the staminate catkin. Sometimes the fertile flowers, though close together, are raised on a rather long peduncle, a condition well shown by our swamp white oak (Quercus bicolor) and the English oak (Q. pedunculata, or Q. Robur pedunculata). Several groups of Mexican and Central American white oaks have similarly long-peduncled acorns, e.g., those centering about Q. macrophylla, Q. peduncularis and Q. reticulata. In some of these, as in an exceptional ally of our own southern live oak Q. virginiana, occasional acorns occur along the peduncle; and in Q. decipiens of the eastern Sierra Madre these are frequent enough and the rachis is long enough to make the inflorescence in fact a sort of loose spike or catkin.

All of these belong to the section of white oaks, Leucobalanus, which are characterized technically by their short broad stigmas, basal abortive ovules, and the glabrate interior of the acorn shell.

The purpose of this paper is to make known three black oaks of the southern Mexican mountains which are quite unique in their section of the genus in bearing their fruit in racemes—or more properly spike-like clusters. They possess the technical characters of the black or red oak section, Erythrobalanus: elongated spatulate stigmas, subapical abortive ovules, and acorn shells tomentose within; but they differ from most black oaks and agree with all white oaks in maturing their fruit in the course of the season of

PROC. AMER. PHIL. SOC., VOL. LX, C, JULY 25, 1921.

flowering instead of deferring fertilization and maturation of fruit for a year.

The first of these species was collected by Dr. J. N. Rose of the United States National Herbarium in the mountains of Tepic in 1897; the second, by Monsieur E. Langlassé in the Sierra of Michoacan or Guerrero in 1899; and the third, by Professor C. Conzatti of Oaxaca in the southern Cordillera in 1907. They constitute a natural group which in some respects suggests relationship with that embracing Q. crassifolia, Q. fulva and Q. stipularis, which likewise mature their fruit in the first season though differing greatly in some other respects. The common and differential characters of these new species may be stated thus:

Racemiflorae.-Moderately large

with stout

tomentose twigs,

rounded buds, large cordate pandurate-obovate or orbicular concave aristately dentate petioled leaves impressed-veiny above and tomentose beneath, and small annual fruit in elongated raceme- or spike-like catkins, the thin cupules with tomentose scales.-Western Sierra Madre and southern Cordillera of Mexico.

Petioles long (20-30 mm.).

Leaves longer than broad, somewhat repand.... Leaves isodiametric, aristate from the nerves. Petioles short (scarcely 15 mm.): leaves isodiametric.

Quercus (Erythrobalanus) Urbani n. sp.

Q. Urbani.

.Q. radiata

Q. Conzattii.

A tree 8-10 m. high, with tortuous trunk. Twigs stout, with dense yellowish tomentum persisting through the second season. Buds rounded, somewhat tomentose. Leaves large (15x 16 cm.), deciduous, pandurate-subobovate, shortly acuminate, cordate-auriculate, lightly hollowed between the aristate ends of the veins, convex, glossy and glabrous except for the impressed veins above,. densely creamy-tomentose beneath; petiole yellow-tomentose, 3 x 25 mm. Flowers unknown. Fruit annual, small, in yellow-tomentose spikes 80-110 mm. long, densely flowered toward the end; cup small (10 mm.), hemispherical, with thin appressed blunt fulvous-tomentose scales; acorn ovoid, 10 mm. long, canescent.

Called encino cucharilla, from its deeply spoon-shaped leaves. Western Sierra Madre of Mexico, at 1,800 m. (Langlassé, 1066, June 20, 1899), from Michoacan or Guerrero,-the type in the herbarium at Dahlem, for the privilege of studying which I am indebted. to Professor Ignaz Urban, of that institution.

[graphic][subsumed][merged small]
[graphic][ocr errors][ocr errors][subsumed][merged small][ocr errors][merged small]
« ПредыдущаяПродолжить »