Splitting Echinocactus: morphological and molecular evidence support the recognition of Homalocephala as a distinct genus in the Cacteae Author Vargas-Luna, Mario Daniel Author Hernandez-Ledesma, Patricia Author Majure, Lucas Charles Author uente-Martinez, Raul Author cias, Hector Manuel Hernandez M Author una, Rolando Tenoch Barcenas text PhytoKeys 2018 111 31 59 http://dx.doi.org/10.3897/phytokeys.111.26856 journal article http://dx.doi.org/10.3897/phytokeys.111.26856 1314-2003-111-31 FF91FFF1FFEDFFA5741A3368FFE6B24D 1492972 Homalocephala polycephala subsp. xeranthemoides (J.M. Coult.) Vargas & Barcenas comb. nov. Echinocactus polycephalus Engelm. & J.M. Bigelow var. xeranthemoides J.M. Coult. in Contr. U.S. Natl. Herb. 3(7): 358. 1896 [1 Apr 1896]. Type. U.S. A., Arizona, near the Rio Colorado, Siler s/n., Nov., 1881 ( lectotype , designated by Benson, Cacti U. S. Canada, 951. 1982: MO 106798 [excluding packet labeled "Siler, 1882"]). Key to genera of HEA clade
1 Stem epidermis glabrous; ovoid to almost circular seeds; campilotropous or anatropous embryos and rounded or acute cotyledons 2
- Stem epidermis pubescent; navicular seeds; orthotropous embryos and obtuse cotyledons Astrophytum
2 Stem apex with scarce trichomes; acute ribs; slightly tubular flowers; campilotropous embryos and acute cotyledons Homalocephala
- Stem apex with a dense cover of trichomes; obtuse ribs; campanulate flowers, anatropous embryos and rounded cotyledons Echinocactus
Key to species of Astrophytum
1 Areoles in mature plants with conspicuous spines 2
- Areoles in mature plants with inconspicuous spines 3
2 Stiff straight spines and completely yellow flowers A. ornatum
- Fexible curved spines and yellow flowers with a reddish base A. capricorne
3 Stems ribbed 4
- Stems tuberculated A. caput-medusae
4 Stems globose to cylindrical, commonly with five acute ribs A. myriostigma
- Stems depressed, commonly with eight obtuse ribs A. asterias
Key to species of Homalocephala
1 Stems rarely to frequently caespitose; yellow flowers and dry fruits 2
- Stems Simple; pink flowers and juicy fruits H. texensis
2 Stems rarely caespitose; yellow flowers with a clear reddish base H. parryi
- Stems commonly caespitose, forming large clumps; yellow flowers without a reddish base 3
3 Spine epidermis and pericarpel scales pubescent; testa cells with periclinal walls with convex relief (papillated) H. polycephala subsp. polycephala
- Spine epidermis and pericarpel scales glabrous; testa cells with periclinal walls with inconspicuous relief (flat) H. polycephala subsp. xeranthemoides
Key to species of Echinocactus
1 Mature plants with stems large globose to barrel shaped with up to 60 ribs; yellow flowers; testa cells with inconspicuous relief E. platyacanthus
- Mature plants with stems depressed, globose to rarely short cylindrical frequently with eight ribs; pink to crimson flowers, seeds with testa cells with a convex relief 2
2 Seedlings with 1 to 2 spines per areole; mature plants with frequently depressed stems; straight spines and light pink flowers E. horizonthalonius subsp. horizonthalonius
- Seedlings commonly with 4 spines per areole; mature plants frequently with short cylindrical stems; curved spines and pink to crimson flowers E. horizonthalonius subsp. nicholii