Mammillaria of the Month

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M. roemeri sp. nova

Mammillaria roemeri is a very recently described species, about which there is still some difference in views about whether it is a good species, or a subspecies or simply an aberrant form of one of the Mammillaria lasiancantha group species, as has been suggested. For reasons of flower position, its placement within Mammillaria is best regarded as uncertain.

It was first described by Kruger and Richser in MafM 2002 and was found in the State of Zacatecas in Mexico. Its body is described as depressed globose, sunken apically, solitary or clumping, 10 - 20 mm high and to 35 mm in diameter. Tubercles are conical, somewhat soft, dark green to brownish green, 3 - 4 mm long, 2 - 3 mm in diameter. It has naked axils, and the sap is without milk. It possesses 25 - 32 spines, radiating, straight or curved, strongly pubescent, glassy white, 1.5 - 2.3 mm long, soft, but central spines are absent. The flower is funnelform, 13 - 15 mm long and wide, whitish to cream- colored with green flush. Inner petals with pink midveins on the sepals. Stigmas are yellow. The fruit is green, 3 - 4 mm long and 3 mm wide. The seed is black, spherical, 1.1 mm long and 0.95 mm in diameter.

The photo above is of a grafted plant, which flowered in April 2007 for the first time. As can easily be seen the placement of the flowers is very different from typical lasiacanthae species, in which the bud emerges from axils very close to the apex, of the plant. Mammillaria roemeri presents its flowers from older areoles, mid way down the body of the plant, in the fashion of Mammillaria crucigera or huitzlipochtlii, although it must be emphasised there is no suggestion of kinship between it and these. It is quite unusual in that in habitat it flowers between November and January, although the photo above was taken in the UK in mid April 2007, although as can be seen, it is on a graft, which might have changed the plants natural cycle.

The plant shown above is solitary, although a sister plant, also grafted had sprouted significantly. This plant was degrafted successfully, and appears to form a rather tighter shape than the flowering plant shown above. It is probably 2 years from seed, grafted in its first year, acquired as a grafted seedling in the summer of 2006.

It doesn't appear too difficult to grow, as three seedlings from Koehres seed, germinated in the Spring of 2007 have grown well in their first year. Germination though was only 30%, based on 10 seeds sown. Time will tell as to how long these will require to develop into flowering plants, especially as they were not grafted but grown on their own roots from seed.