Xerophyte

Central Spines

4, cruciform, brown with a dark point, 8-10 mm long, the lower being the longest, hooked, the upper three straight.

Seeds

1.1 mm black.

Description

Mammillaria louisae is a most alluring miniature species distinguished by its extremely large flowers that may exceed the size of its small vegetative body. The flower is white or light pink with a darker stripe down the center. The dwarf globular body is usually solitary and is covered with light brown radial spines and 4 dark brown centrals of which one is hooked. Sometimes we find the spelling "louisiae".

Taxonomy

M. louisae has historically been confused confused with other Mammillaria taxa especially with Mammillaria hutchinsoniana, which is a larger plant that occurs farther south and inland. The Mammillaria species of Baja California are understudied and there is no single key to all taxa. Identification difficulties obscure our understanding of the range and rarity of taxa such as M. louisae. Several individuals appear to be morphologically intermediate or do not fit cleanly within existing species descriptions [6].

Roots

Fibrous, with no distinctly enlarged tap root.

Note

George Edmond Lindsay named the plant Mammillaria louisaeSN|5426]]SN|5426]] in December 1960 in honour of Louisa Hutchison (fl. 1934), mother of the US-American cactus collector Ted Hutchison.

Tubercles

5-6 mm long, 4 mm broad at the base, the axils bearing white felt when young but no bristles or spines.

Flowers

Flowers in a ring about the crown, arising from the axils of the tubercles, fairly large compared to the size of the plant (up to to 3.5 cm long and 4 cm across). Pericarpel scaleless. Perianth segments grading from small scales near the base of the tube to the inner perianth segments; outer segments olive to brownish green with light pink margins; inner segments whitish or pinkish, with lavender-pink, or brownish-pinkish median streak to 25 mm long and 6 mm. wide. The protruding stigma has 6-8, lobes 7-11 mm long, olive-green or reddish brown. M. louisae is interesting in that the stigma lobes are quite hairy when inspected under a hand lens. Mammillaria louisaeSN|5426]]SN|5426]] flowers in the hottest months. The flowers close at night but reopen a second day.

Stem

Usually solitary or occasionally branched, dwarf globular, 1 to 3.5 cm. tall and 1.5 to 3 cm. wide occasionally reaching a maximum of 6 cm in height for 4 cm in diameter. Greyish green almost completely hidden by the spines.

Radial Spines

Between 10 and 20, acicular, 5-7 mm. long, white or light brown with dark tip.

Fruits

Large, round to clavate, to 20 long, and 4 (or more) mm wide, brick red. M. louisae both in habitat and in cultivation flowers and fruits freely.

Areoles

Round, about 1.5 mm in diameter, bearing white felt.