INTERGENERIC HYBRIDS IN THE MEXICAN CRASSULACEAE. IV. VILLADIA


CHARLES H. UHL

Plant Biology,

Cornell University,

Ithaca, NY 14853-5908


Natural hybrids between species of the Mex­ican Crassulaceae are very uncommon in nature, and I know of fewer than ten. However, most species hybridize readily in cultivation, and I have produced hybrids that combine more than 200 species and perhaps nine genera, directly or indirectly, into a biosystematic unit called a comparium, certainly one of the largest known.


Earlier papers in this series have listed intergeneric hybrids, some of them new, of Leno­phyllum (Uhl, 1993) and Thompsonella (Uhl, 1994b) and have discussed the probable absence of genuine hybrids between Dudleya and other genera (Uhl, 1994a). This paper reports 16 hy­brids involving eight species of Villadia and nine species of five other genera, with four of the intergeneric combinations reported and named here for the first time. Seventy-six other attempts at intergeneric hybrids of Villadia, including all nine with Thompsonella, all four with Lenophyllum, and the only one with Dudleya, yielded no hy­brids.


Berger (1930) assigned Villadia and Leno­phyllum to subfamily Echeverioideae, but both genera have terminal (vs. lateral) inflorescences, and in this and other respects they seem much more closely allied to the subfamily Sedoideae. Vegetatively and in their flowers they differ so much from the other genera of Berger's Echeveri­oideae that hybridization might seem unlikely, but I have earlier (Uhl, 1993) reported hybrids of Lenophyllum with Graptopetalum, Echeveria and Pachyphytum, and I have crossed Villadia with the same genera and also with Cremnophila.


Villadia has about 40 species, including sev­eral not yet named, distributed from western Texas (one species) to the Andes of South Amer­ica, with most species in Mexico. Altamiranoa Rose has similar flowers and is generally reduced to Villadia as a subgenus, but it has a more spreading, cymose inflorescence, contrasted with the spike, tight raceme or thyrse in subgenus Villadia. Of the species hybridized, V. grandisepala, V. necaxana and Sedum latifilamentum, which I think is best considered a Villadia, belong with subgenus Altamiranoa, all the others with sub­genus Villadia. The genus is not well understood, and Reid Moran is revising it.


Gametic chromosome numbers in more than 150 collections of about 30 species of Villadia, some of them undescribed, include every number from 9 (in an unidentified collection from Coahuila) through 17, as well as 20, 21, 23, 25, and higher numbers to 88 in plants from Peru (Uhl, mostly unpubl.). No clear basic chromosome number or polyploid series are evident.


All hybrids had parents with different chro­mosome numbers, and they all had highly irreg­ular meiosis with many unpaired and lagging chromosomes, bridges, etc. Few or none of their reproductive cells receive complete and balanced outfits of genes, and by anthesis most of their pollen grains have aborted and are empty ("ghosts"), and they do not slain in aniline blue/ lacto phenol. Most or all of those few that do slain (and therefore were still alive) are abnormal in size and/or shape and certainly not functional. Judging from the appearance of their pollen, all of the hybrids are probably highly sterile, except possibly for one tetraploid and a couple of triploids.


Herbarium specimens of all parents and hybrids are in the Bailey Hortorium of Comell Uni­versity, and color photographs and slides of the chromosomes and pollen of most of them also are available.



Figs. 1, 2. Cremnophila nutans (Moran 10174 x V. nelsonii (Moran 10109).


x Cremnadia Uhl, new nothogenus


I propose this name for all hybrids between Villadia Rose and Cremnophila Rose. Some au­thors do not accept Cremnophila as a genus and instead separate its two very similar species into Sedum and Echeveria.


Cremnophila nutans (Moran 10174, n = 33) x Villadia nelsonii (Moran 10109. n = 20). (Figs. 1, 2). Meiosis is very irregular, with 10-14 paired elements plus 16-27 unpaired in 8 cells at metaphase I. 0.5% of pollen stained.


Five other crosses were unsuccessful.



Figs. 3, 4. V. grandisepala {C48-35) x Echeveria chapalensis (U2140).


x Villeveria Uhl, new nothogenus


I propose this name for all hybrids between Villadia Rose and Echeveria DC.


Villadia grandisepala (Clausen C44-35, n = 44) x Echeveria chapalensis (U2140, n = 45).

(Figs. 3. 4). Both parents are polyploid. and live cells at metaphase I in the hybrid showed 33-40 paired elements plus 2-7 unpaired. Some pollen stained and a few grains looked normal.


Three other possible villeverias died as seed­lings before their hybrid identity could be con­firmed, and one other attempted cross was un­successful.



Figs. 5, 6. Graptopetalum fruticosum (U1078) x V. sp. (U1441)


x Graptoladia Uhl, new nothogenus


I propose this name for all hybrids between Villadia Rose and Graptopetalum Rose.


Graptopetalum fruticosum (U1078, n = 31) x Villadia sp. (U1441, n = 14). (Figs. 5, 6). Few chromosomes paired at meiosis. and no pollen stained.


G. fruticosum (U1398, n = 31) x V. sp. (U1855, n = 20). U1855 is Sedum latifilamentum Clausen, which I think is really a villadia of subgenus Altamiranoa (Uhl, 1985), and so I list it here. One of 16 seedlings from this cross appeared genuine and survived for ten years without flowering-the other 15 re­sembled the seed parent and evidently re­sulted from self-pollination.


Six other attempted crosses involving three species of Graptopetalum and five species of Vil­ladia were unsuccessful.



Fig. 7. Pachyphytum hookeri (Moran 13349) x V. sp. (Moran 10107).



Fig. 8. Pairs of flowers of Pachyphytum hookeri (Mor­an 13349) (left), V. sp. (Moran 10107) (right), and their hybrid (center).


x Pachyladia Uhl, new nothogenus


I propose this name for all hybrids between Villadia Rose and Pachyphytum Link, Klotzsch and Otto.


Pachyphytum hookeri (Moran 13349, n = 32) x Villadia sp. (Moran 10107, n = 14). (Figs. 7, 8). Meiosis is highly irregular, with 20 or more chromosomes unpaired. Moran 10107 and U1441 (cited above as parent of a hybrid with Graptopetalum fruticosum} are collec­tions of the same, probably undescribed vil­ladia.


P. hookeri (Moran 13349, n = 32) x V. nelsonii (Moran 10109, n = 20). 8-14 paired chro­mosomal elements plus 24-35 unpaired in 8 cells at metaphase I. Some cells may have no pairing.


Eight other attempts to cross P. hookeri with seven species of Villadia were unsuccessful.



Figs. 9, 10. Sedum craigii (U1206} x V. nelsonii (U2372).


xSedadia Moran


Moran (1975) named xSedadia for Sedum amecamecanum, which appears to be Sedum dendroideum ssp. monticola (=S. praealtum ssp. monticola) x Villadia batesii, one of very few natural hybrids among the Mexican Crassulaceae. Plants of xSedadia amecamecanum in the wild were intermediate and closely associated with the putative parents (Clausen, 1959). It is sterile, and study of its chromosomes offers strong support for this hybrid origin (Uhl, 1978). I have produced ten other hybrids between Sedum and Villadia, and I am sure that many others are possible.


Like the more "typical" sedums, Villadia has terminal floral stems, and nine of its ten hybrids listed here are with "typical" species of Sedum. Only S. craigii has lateral floral stems and be­longs with subgenus Pachysedum.


Sedum alamosanum (U1647, n = 18) x Villadia ramosissima (U1455, n = 15). Meiosis is very irregular. Less than 5% of pollen stained. most of it abnormal.


S. alamosanum (U1647, n = 18) x V. sp. (U1855 = Sedum latifilamentum, n = 20). I consider S. latifilamentum to be a villadia (Uhl, 1985), and so I list this as an intergeneric hybrid. Very few chromosomes pair at mei-osis.



Fig. 11. Pairs of flowers of Sedum alamosanum (U1647) (left), V. cf. guatemalensis (Moran 7752) (right), and their hybrid (center).


S. alamosanum (U1647, n = 18) x V. cf. guatemalensis (Moran 7752, n = 20). (Fig. 11). Very little chromosome pairing, and many anthers degenerate. Less than 1% of pollen stained.


S. craigii (U1206, n = 30) x V. nelsonii (U2372, n = 20). (Figs. 9, 10). About 12-18 paired elements and 11-26 unpaired in 8 cells at metaphase I. 9% of pollen stained, but most of this was abnormally large and possibly unreduced.


S greggii (Moran 7807, n = 33) x V. aperta (U2255, n = 15). Meiosis is highly irregular. with 20 or more unpaired chromosomes. 20% of pollen grains stained, but few were normal.



Fig. 12. Pairs of flowers of Sedum greggii (U1491) (left), V. sp. (Moran 10107} (right), and their hybrid (center).


S. greggii (U1491, n = 33) x V. sp. (Moran 10107. n = 14). (Fig. 12). Meiosis is highly irregular.


S. greggii (Moran 14730, n = 26) x V. cf. guatemalensis (Moran 7752, n = 20). Some pol­len mother cells degenerate before meiosis. The S. greggii seed parent of this hybrid closely resembles the S. greggii seed parents of the two preceding hybrids, but the differ­ence in their chromosome numbers suggests that biologically they should be classed as different incipient species (Uhl, 1985).


V. grandisepala (Clausen 48-35, n = 44) x S. obcordatum (U1583, n = 34). This triploid hybrid formed 26-32 total chromosomal el­ements of all kinds in 5 cells at metaphase I. 59% of pollen stained; some looks normal.


V. grandisepala (Clausen 48-35, n = 44) x S. alamosanum (U1647, n = 18). This triploid hybrid looks more like its tetraploid parent and formed 18-22 paired elements plus 9-16 unpaired in 17 cells at metaphase I. Some pollen looks normal.


V. nelsonii (Moran 10109, n = 20) x S. palmeri (U1367, n = 34). About 14-18 paired ele­ments plus 10-19 unpaired at metaphase I and up to 4 bridges at anaphase I. 2% of pollen stained, mostly abnormal.


Thirty-four other crosses, involving 14 species of Sedum and seven of Villadia, were unsuc­cessful.


Seven additional hybrids, involving five of the above species, had villadias as both parents. An­other hybrid, V. nelsonii (Moran 10109, n = 20) x V. necaxana (probably best regarded as a gla­brous form of the otherwise hairy V. elongata) (U1555, n = 23) represents a cross between subgenus Villadia and subgenus Altamiranoa, and it adds one more species to the comparium. Mei­osis was irregular and only about 1% of pollen stained. Eight other attempts to cross different villadias with each other were unsuccessful.


References


Berger, A. 1930. Crassulaceae. In: A. Engler, Die natürlichen Pflanzenfamilien, 2nd ed. 18a: 352-485.

Clausen, R. T. 1959. Sedum of the trans-Mexican volcanic belt. Ithaca, NY

Moran, R. 1975. New names and combinations in Crassulaceae. Baileya 19: 145-147.

Uhl, C. H. 1978. Chromosomes of Mexican Sedum II. Section Pachysedum. Rhodora 80: 491-512.

———. 1985. Chromosomes of Mexican Sedum V. Section Sedum and subgenus Sulcus. Rhodora 87: 381-423.

———. 1993. Intergeneric hybrids of Mexican Cras­sulaceae I. Lenophyllum. Cact. Succ. J. (U.S.) 65: 271-273.

———. 1994a. Intergeneric hybrids of Mexican Cras­sulaceae II. Dudleya. Cact. Succ. J. (U.S.) 66: 74-80.

———. 1994b. Intergeneric hybrids of Mexican Cras­sulaceae III. Thompsonella. Cact. Succ. J. (U.S.) 66: 175-179.


© Cactus & Succulent Journal of America, 1994