Manihot oaxacana D.J.Rogers & Appan

  • Authority

    Rogers, David J. & Appan, S. G. 1973. Manibot, Manihotoides (Euphorbiaceae). Fl. Neotrop. Monogr. 13: 1-272. 1 chart. (Published by NYBG Press)

  • Family

    Euphorbiaceae

  • Scientific Name

    Manihot oaxacana D.J.Rogers & Appan

  • Type

    TYPE. Rogers 505: Mexico, Oaxaca: 17 km ENE of Juchitan, 22 Jul 1963 (holotype, NY; isotypes, COLO, F, G, K, MEXU, MO, P, S, SP, UC, US, W).

  • Description

    Latin Diagnosis - Frutices 2.0-5.0 m altae, glabrae; folia septemloba, lobus medianus ca 10.0 cm longus, ca 4.0 cm latis; inflorescentia racemosa, brevis, ca 5.0 cm longa; flores staminati conici; capsulae ca 1.5 cm longae; semina ca 0.9 cm longa.

    Description - Arborescent shrubs, 2.0-5.0 m tall, trunk diam ca 10.0 cm, branching begins above the middle, dichotomously and trichotomously branching, branches with a tendency to spread out. All parts of the plant with strong odor of HCN. Roots slightly swollen; epidermis rough, strong brown (5 YR 4/5) subepidermis white. Young stems glabrous, strong brown (5 YR 4/5), internally light yellow-green (7.5 GY 9/4); mature stems brownish gray; latex cream colored. Young foliage at apex strong yellow-green (7.5 GY 6/8). Leaves alternate, stipules deciduous, glabrous; petioles generally 10.0-15.0 cm long, terete, dull red-green with some olive shading; lamina nonpeltate, ventral surface deep green, glabrous; dorsal surface pale green, glabrous, midribs and major veins prominent, abaxial surface wax pattern reticulate; venation camptodromous; palmately 7 lobed, 3 major, 2 smaller, and often 2 minute lobes; median lobes usually ca 10.0 cm long and ca 4.0 cm wide, obovate-pandurate, occasionally obovate, entire lobed, the primary constriction of pandurate lobes shallow to deep, apex varies from almost truncate with an acute conical tip in the middle, to acuminate. Plants begin to flower when ca 1.0 m tall; inflorescence a short, moneocious, axillary raceme, usually ca 5.0 cm long, never longer than 8.0 cm, pedicels comparatively longer at base, gradually decreasing in length towards apex, giving the inflorescence a more or less conical shape, all parts glabrous; bracteoles setaceous, less than 0.3 cm in length, margin smooth; bractlets setaceous. Pistillate flowers restricted to the base of the inflorescence, borne on 1.0-2.0 cm long pedicles, tepals externally brilliant yellow-green (2.5 GY 9/8), cleft to the base into 5 lobes, lobes lanceolate-oblong, disc fleshy, entire, brilliant yellow-green (2.5 GY 9/8), ovary subglobose, entire, the three divisions of the stigma moderately lobed and lobulate. Staminate flowers characteristically conical, often as long as 1.8 cm, tepals brilliant yellowish green externally (2.5 GY 9/8), cleft 1/3 of the way down into 5 lobes, lobes tapering, acuminate, disc 10 lobed, brilliant yellowish green (2.5 GY 9/8), stamens 10, in 2 whorls of 5 each, filaments and anthers white. Fruit pedicels 1.0-2.0 cm long, slightly curved downwards; capsules more or less globular, ca 1.5 cm long from base to apex, surface slightly rugose, with 6 very small wings, apex rounded, fruit dehiscence septicidal. Seeds oblong, ca 0.9 cm long, carunculate and bluntly acute, caruncle moderately prominent.

    Distribution and Ecology - Mexico: Oaxaca. Flourishes in the plains and foothills surrounding Juchitan and Tehuantepec, and upstream on both sides of Rio Tehuantepec; to 150 m. It appears that the range of this species extends upwards as high as 1000 m, towards the headwaters of Rio Tehuantepec. Webster, Miller & Miller 11641, collected at an alt of 870 m, may represent an ecotypic form of this taxon, but the poor condition of the specimen does not render critical comparisons possible. Similarly Conzatti 2413, collected from Quiotepec, Cuicatlan at an alt of 700 m resembles M. oaxacana, but positive identification has not been possible due to the poor condition of the specimen. Further collections from these areas will confirm the possibility of the range of this species extending along the northeastern foothills of the Sierra Madre del Sur, up to Cuicatlan which is on the periphery of the range of Manihotoides pauciflora.

  • Discussion

    This species was confused in the past with Manihot chlorosticta. The former is an arborescent shrub, while the latter is a clambering vine. There are several other features which characterize M. oaxacana such as the very short raceme, conical brilliant yellow flowers, smaller fruits and seeds, etc. Besides, the geographical ranges of these two species are disjunct and consequently there is little likelihood of interbreeding. This Oaxaca population represents a closed gene pool in itself and as such a distinct biological species. Rogers (1965) discovered and defined this population as an undescribed species, based on field study observations. The specific epithet denotes the distribution which is confined only to the state of Oaxaca.

    In the computer analysis Manihot oaxacana cluster joins M. chlorosticta cluster at a "C-value" of .857 and soon both the clusters integrate tightly. The general ecological habitat of both these species is very similar, both flourishing along the coastal belt. All these suggest that these two species are very closely related. Without cytogenetic data it is unsound to hypothesize; nevertheless, it seems obvious that M. oaxacana and M. chlorosticta once belonged to the same ancestral gene pool, eventually splitting and diverging into two closed gene pools. The M. oaxacana population, occupying a pocket confined by mountain barriers, is strongly suggestive of the possibility of a segment of the ancestral gene pool being restrained to evolve independently in isolation.

  • Distribution

    Mexico North America| Oaxaca Mexico North America|