11. SEDUM QUEVAE (figs. 36-40)

Sedum quevae is the only shrubby species of Sedum of the Trans-Mexican Volcanic Belt with tubers. Among the species with peel­ing bark, it is distinctive in having the petals connate basally and the leaves oblanceolate.

Description. Materials: 12 plants-7 from northwest of Malinche in the state of Tlaxcala; 3 from El Tezcal southwest of Tepoztlan, Morelos; and 2 from Lachivía, Oaxaca. Measurements marked cult. are of plants cultivated in the greenhouse at Ithaca, N.Y. Those marked h. are of herbarium specimens and pr. of flowers preserved in 70 percent alcohol.

Fig. 36. Plant of Sedum quevae from near Santa María Atlihuitzía, Tlaxcala, culivated in the greenhouse, Ithaca, N.Y. A. Plant (x ,4). B. Flower from above (x 1.6). C. Flower from side (x 1.6). D. Petal and stamens (x a.4). E. Pistils (x 2.4). F. Single pistil (x 3.2). G. Nectary (x 4). H. Portion of stem and one leaf (x 1.6).

Plants of Sedum quevae are subshrubs with stems much branched and erect or decumbent and with bark on older stems cracking and peeling in thin layers; twigs are finely papillose; rhizomes de­velop clusters of pale brown tubers, these sometimes moniliform. Differences in height and in diameter of tubers are not significant, either among populations or between plants in the wild and in cultivation.

Leaves are oblanceolate or elliptic-oblanceolate, spurred, obtuse, usually rounded, finely papillose, deciduous after plants have flowered. Plants from El Tezcal sometimes have the leaves emargi-nate, with the apical sinuses .1-.4 mm. deep, but the three plants from there vary in this condition; plants from northwest of Malinche may also have some leaves slightly emarginate. Differences in length and width of leaves and in the condition of the apices, whether among populations or between plants in the wild and those in cultivation, are not significant, except that the leaves of a plant from Lachivia are much longer and wider than those from else­where and those of the cultivated sample from El Tezcal are significantly shorter than those from northwest of Malinche.

Twelve leaves selected from three plants northwest of Malinche on Aug. 23, 1955, measured in fresh condition and then dried as herbarium specimens, had when remeasured on Sept. 1, 1957, an average loss of length of 1.5 mm. and an average1 loss of width of .4 mm. These differences are not significant.

Another sample of ten leaves from a plant al El Tezcal, meas­ured when fresh on Aug. 31, 1955, and again when dried on Sept. 1, 1957, had not changed significantly in length, but had shrunk

significantly in width.

Inflorescences are terminal, pleiochasial cymes.

Flowers are rarely 6-merous and are either sessile or on pedicels <3 mm. long.

Sepals are oblong, minutely spurred, obtuse, papillose, green speckled with red. The difference in length between plants from northwest of Malinche and those from El Tezcal is significant, and the difference in width is highly significant, but neither difference is significant for plants from these localities cultivated in a com­pletely random experiment in the greenhouse.

Petals are lanceolate, acute, minutely mucronate-appendaged, white, pale green or pink on dorsal keels above middle and also papillose on dorsal keels. The difference in length is significant between plants northwest of Malinche and those at El Tezcal, and the difference in width is highly significant, but these differ­ences are not significant when plants from the two localities are grown under similar conditions.

Stamens have white filaments and red anthers; pollen is well developed.

Nectaries are thick, subquadrate or reniform, truncate, while or very pale yellow, rarely pinkish. Differences in width between plants from northwest of Malinche and those from El Tezcal are significant both in the wild and in cultivation under similar con­ditions, but in the wild the nectaries of plants from El Tezcal are narrower and in cultivation wider than those of plants from north­west of Malinche.

Pistils are erect and white or greenish white. One flower of a plant from El Tezcal, otherwise 5-merous, had only 4 pistils.

Follicles are erect and pale brown or reddish brown.

Seeds are elliptic-oblong, smooth, and yellow-brown.

Variation. Before consideration of the variation of Sedum quevae, more information is necessary concerning the origin of the plants on which the comments are based. The sample in cultivation from northwest of Malinche comprises six plants. One is from near the waterfalls at Santa Maria Atlihuitzia; three are from a quadrat 1 if 2 sq. m. on the bank of the road near San Bernabe, about 6 km. northeast of Tlaxcala and about 2.5 km. south of Santa María Atlihuitzía; and two are from Santa Elena, about 2 km. northeast of San Bernabé and about 8 km. northeast of Tlaxcala. Cultivated in ihe greenhouse, these six plants differ in at least eight characters. In all except one of the eight characters, the greatest differ­ences exist among the three plants selected from the quadrat. The greatest difference in the eighth character was between the two plants from Santa Elena. Instead of samples from different sites varying from each other, the greatest differences are among plants from the same site. A plant 1 m. east of the quadrat on the bank near San Bernabé appears to be a sterile hybrid between S. quevae and Villadia scopulina. The possibility exists that the variability among plants of apparent S. quevae may be the result of backcrossing; but in only two characters, namely, length of petals and pistils, is the variation of the three plants at San Bernabé in the direction of the Villadia. Further, the sterility of the hybrid does not suggest that backcrossing is likely. Another plant, apparently also a hybrid, from Santa Elena, similarly is sterile.

The population at El Tezcal appears to be small and homoge­neous. The three plants studied are similar. Two of these are the most widely separated plants in the population, about 12 m. apart; the third is from within 1 dm. of the second. On the basis of study in the field, the plants at El Tezcal are not the same as those northwest of Malinche, differing significantly in five characters, namely, in length and width of both sepals and petals and in width of nectaries. Such evidence suggests possible subspecific distinction, but when plants of both populations are grown under similar con­ditions, the differences disappear except the one concerned with the nectaries; in addition, the leaves of plants from El Tezcal are significantly shorter. Whereas the nectaries are significantly nar­rower in the field, they are significantly broader in the greenhouse. The nectaries of the plants from northwest of Malinche are of the same average width both in the field and in the greenhouse. An opinion whether the population at El Tezcal is a distinctive subspecies should await further exploration for other possible populations and should also await more adequate sampling of the known populations of Sedum quevae.

A plant from Lachivía has longer, wider leaves than those from elsewhere. Possibly a subspecies with larger leaves exists in the Sierra Madre del Sur, but before judgment is possible, informa­tion is necessary concerning the variances of dimensions of leaves among plants in the population at Lachivía or elsewhere in the area of occurrence. Once the variances among plants are known, an estimate will be possible of what should be an adequate sample from there. Until such a sample has been studied, appraisal of the subspecific status of plants from Lachivía must remain uncertain.

Nomenclature. Sedum quevae Raymond Hamet, Bot. Jahrb. 50, Beibl. 114: 25-26 (1914). Type locality. Aseseca, Puebla. Type: Arsene's no. 193, collected Nov. 20, 1906, reported to be in the herbarium of the University of Montpellier. I have not seen the type, but have studied specimens from other localities, all in Puebla, cited by Hamet in the original description: Acatzingo Cerro Guadalupe, Hacienda Alamos and ravines near that ha­cienda. Details of the original description are in agreement with the data for my samples described above. Hamet named the species for Professor Queva of the University of Dijon, in whose laboratory he studied.

A synonym is:

1918. Sedum falconis T. S. Brandegee, Univ. Calif. Pub. Bot. 6: 498 Type locality: rocks, Cerro del Gavilan, near San Luis Tultitlanapa, Puebla. Type: Carl Purpus' no. 4,227, collected in August, 1909 (UC 136,828). Fröerström (1930-1935, pt. 4, pl. 21) published a photo­graph of the type.

Sedum arsenii (Fröerström, 1930-1935, pt. 4, p. 30) was never validly published.

Distribution. Sedum quevae occurs in the southern part of the Trans-Mexican Volcanic Belt, from the region of Acatzingo west-southwest of the peak of Orizaba west to El Tezcal northeast of Cuernavaca, and also in the central part of the Sierra Madre del Sur, at Lachivía, Oaxaca. I have studied in the field the two popu­lations listed below:

Fig. 37. Part of known distribution of Sedum quevae.

Other populations and the discoverers of each are: "Aseseca, Arsene (Montpellier)"; Acatzingo, Arsene (US); vicinity of Puebla, Arsene (US); and Cerro del Gavilan, Carl Purpus (UC).

In the region northwest of Malinche, Sedum quevae occurs on conglomerate in small groups of about 20 plants per site. Exposure is to the north, northwest, and southeast. In 1954, Edward Alexander told me about a Sedum with while flowers, in bloom on Aug. 26, 1945, which grew near San Bernabé, east of Tlaxcala. Possibly that was S. quevae. I have studied plants in that region in 1949 and again in 1955. At Santa María Atlihuitzía, domestic animals eat the tender new shoots of the Sedum. All plants there either were under the protection of thorny branches of leguminous shrubs or were on steep, rocky slopes. Plants there and at San Bernabé had floral buds on Aug. 23, 1955. On Oct. 18, some were in flower. Competing species at San Bernabé included Barbula spiralis (identified by Professor Andrews), Notholaena aurea, Ipomaea (?longipedunculata), Stevia paniculata, Aegopogon tenellus, a shrubby mint, and Villadia scopulina.* At Santa Elena, besides V. scopulina, other Crassulaceae within 200 m. of S. quevae were S. moranense and V. misera, the latter in flower on Aug. 23, 1955.

I first saw Sedum quevae at El Tezcal, about 9 km. southwest, of Tepoztlan, on Aug. 30, 1955. At that time, the plants had floral buds, but S. jaliscanum, growing in the same habitat on the lava, was in anthesis. By Nov. 17, S. quevae was in anthesis, and all plants of S. jaliscanum were withered and in fruit. No other Crassu­laceae were in the vicinity. Exposure of plants of S. quevae was to the east and northeast. Common competing species on the lava included Prionosciadium nelsonii, Dahlia coccinea, and Jaegeria hirta.

Relationships. On the basis of gross morphology, species re­lated to Sedum quevae are S. oxypetalum, S. frutescens, S. tortuosum, S. retusum, and S. tuberculatum. All are subshrubs with papillose twigs and leaves broader than thick. Sedum quevae differs from all of these in having tubers, petals which are connate basally, and follicles which are erect, with margins not markedly enlarged as corky ridges. Plants of S. frutescens and S. oxypetalum have stout trunks. Sedum tortuosum is an epiphyte with long, winged seeds. Sedum retusum has prominently retuse leaves, petals which usually are pink basally, orange nectaries, pink ovaries, and papillose seeds. Sedum tuberculatum has oblanceolate sepals and yellow nectaries. Since none of the supposedly related species occur at the same sites with S. quevae, hybridization cannot occur.

The two apparent hybrids between Sedum quevae and Villadia scopulina indicate another relationship. In the field, I thought that both plants were S. quevae. Since I did not appreciate the signifi­cance of these two plants and was not investigating Villadia at the time of their discovery, I neither studied variation in the popula­tion of V. scopulina nor collected more than one plant of it for culture. The hybrid at Santa Elena had remarkably narrow leaves, apparently an etiolated condition resulting from growth in the shade of a narrow ravine. I confidently expected that this plant would have broader leaves when grown in the greenhouse in an experiment with other samples of S. quevae. Instead, it continues to differ in its narrower leaves from S. quevae. It flowers profusely in the greenhouse, and its petals become spotted with red pigment from the anthers. Evidently the cells of the tissue of the anthers break down, with the result that the red pigment diffuses. Pollen does not develop, and the ovules abort. At both places where I found the supposed hybrids, S. quevae and V. scopulina occur near together, within 2 m. of each other at each site. Plants of the two species flower at the same time, namely, at the end of the wet season. The characteristics of the supposed hybrids are a re­combination of those of the suspected parental species, but transgressive in length of sepals, as shown in the following table in which all data are for plants grown under similar conditions in the greenhouse at Ithaca.

Fig. 38. Villadia scopulina, Sedum quevae x V. scopulina, and S. quevae, from left to right, all from northwest of Mt. Malinche, cultivated in the greenhouse, Ithaca, N.Y., Oct. 5, 1956 (ca. x .1).

The sepals of the hybrids are longer and wider than those of plants of either parental species. Further, the petals are longer.

Fig. 39. Flowers of Sedum quevae (left) and S. quevae x Villadia scopulina (right) from plants cultivated in the greenhouse, Ithaca, N.Y., May 31, 1956 (x 4.3).

The hybrids and Villadia scopulina differ from Sedum quevae in three characters, but on the other hand they and S. quevae differ from the Villadia in one character. Four differences between the two hybrid plants suggest that they are different genetically, probably the result of independent crossing of different biotypes of either or both parental species. Variability among the five plants of the sample of S. quevae from northwest of Malinche may be the result of backcrossing of F1 hybrids, but since these appear to be sterile, it may also be the result of gene mutation within S. quevae.

Fig. 40. Sedum, quevae x Villadia scopulina, two plants from northwest of Mt. Malinche, from San Bernabé (left) and Santa Elena (right), cultivated in the greenhouse, Ithaca, N.Y., May 31, 1956 (x 2.4).

* Villadia scopulina, (Rose) comb. nov., fundata super Altamiranoa scopulina Rose, Bull. N.Y. Bot. Gard. 3: 32 (1903).

© Sedum of the Trans-Mexican Volcanic belt, 1959