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Subfamilia Cactoideae, tribus Cacteae
The type is Sclerocactus polyancistrus.
The genus name derives from the Greek scleros meaning hard, (referring to the hard seed tegument or to the formidable hooked spines), so the name means "hard cactus".
The genus Sclerocactus contains 19 species 5 subspecies according to The New Cactus Lexicon (2006) by International Cactaceae Systematics Group (ICSG).
According to ICSG, the genera Toumeya, Ancistrocactus, Glandulicactus, Coloradoa and Echinomastus are lumped into the genus Sclerocactus.
Despite the extensive field researches, there is a debate about defining the correct boundaries of the genus still.
As to E.F.Anderson (The Cactus Family, 2001), Echinomastus is a seperate genus because of the results of the DNA sequencing analysis by J.M. Porter (1999), morphological structures and Anderson's own field studies. But some new molecular evidence broadly supports the circumscription of the genus Sclerocactus thus the lumping Echinomastus and other genera in this genus.
As to NCL, there are 3 subgroups of the genus:
group 1 Ancistrocactus (including Glandulicactus)
S.brevihamatus, S.scheeri, S.uncinatus
group 2 Echinomastus
S. erectocentrus, S. intertextus, S.mariposensis, S. unguispinus, S.warnockii
group 3 Sclerocactus
S.glaucus , S.johnsonii , S.mesae-verdae, S.nyensis, S.papyracanthus, S.parviflorus, S.polyancistrus, S.spinosior, S.pubispinus, S.whipplei, S. wrightiae.
For curious readers, some well known varieties before lumping:
S.erectocentrus: Echinomastus acunensis.
S.unguispinus: E.durangensis,E.mapimiensis, E. laui.
Many species of the Sclerocactus have restricted distributions and have been badly affected by illegal collecting.
Most of the Sclerocactus have tuberculated, weekly ribbed stems, grooves on the upper side of the tubercles and extrafloral nectary glands on the extended areol beyond the spine bearing portion (gland-spines). Flowers arise from the apex, diurnal and in spring-summer. This impressive group of small cacti from SW USA and N Mexico is very difficult to propogate.
The caring of Sclerocactus species in cultivation is quite difficult on its own roots and also to propagate from seeds. The mature plants and seedlings rot very easily and the germination rate of the seeds is very low. So, they are usually grafted on a frost hardy stock. Here , I treated the genus as to The New Cactus Lexicon (2006).
SPECIES and SUBSPECIES LIST
1 S.brevihamatus ssp.brevihamatus 1a S. brevihamatus ssp.tobuschii 2 S. erectocentrus 3 S. glaucus 4 S.intertextus 5 S.johnsonii 6 S. mariposensis 7 S. mesae-verdae 8 S. nyensis 9 S. papyracanthus 10 S. parviflorus 11 S. polyancistrus 12 S. pubispinus 13 S. scheeri 14 S. spinosior ssp.spinosior 14a S. spinosior ssp.blainei 15 S. uncinatus ssp.uncinatus 15a S. uncinatus ssp.crassihamatus 15b S. uncinatus ssp.wrightii 16 S.unguispinus 17 S. warnockii 18 S. whipplei ssp.whipplei 18a S. whipplei ssp.heilii 19 S. wrightiae
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Sclerocactus unguispinus 'durangensis' SB322 06