Species Notes:Comment from Gottfried Unger -Author, "Die grossen Kugelkakteen Nordamerikas":
...in the book of Mr. Anderson alamosanus and reppenhagenii are treated as two subspecies under F. alamosanus. Anderson's decision is based on N.P. Taylor's opinion. But there are many reasons to accept the two taxa as different species. However, they belong to a group of five closely allied species. The group is: F. alamosanus, F. schwarzii, F. reppenhagenii, F. glaucescens, & F. echidne. Of these the first 3 together with F. pottsii (not related to them) very often are still objects of great confusion. These plants need careful study. Most of the characteristics where unknown until recently. While the areas (locations) of F. alamosanus and F. schwarzii in the states of Sonora and Sinaloa, Mexico to our knowledge are very limited but close together, the area (location) of F. reppenhagenii is about 1000 km apart of these two in the states Colima, Michoacan, Guerrero and Oaxaca and therefore is a very large area of some expected variation. However, all these areas (locations) at this time are not well explored. According to the seed characters, the species alamosanus and schwarzii are much closer than alamosanus and reppenhagenii. The first two have sunken depressed testa cells with prominent cell walls around (see micro photo here), while reppenhagenii has no prominent cell walls, the testa cells are nearly flat or evenly raised. This points to a different species. While F. alamosanus and F. schwarzii as old plants are large globular in appearance with many ribs (more than 20), wide open blossoms and spatulate broad petals, and dull brown-red fruits splitting open when ripe, F. reppenhagenii is a plant of a small diameter, nearly cereoid growing, rarely more than 13 ribs, the blossoms small and narrow, the petals lanceolate and acute, the fruits bright red and not splitting when ripe. Finally F. schwarzii versus alamosanus is remarkable for loosing its spines when growing older and older. Taking all this into consideration it seems better to accept all these plants as different species.
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