Based on information by Mr. Gerhard Marx.
Haworthia hammeri (Dr. M. Hayashi) is a relatively recent discovery from the Haworthia mirabilis group, occurring in a small area north-west of the Potberg in the Bredasdorp district. The plants are found on a few small unploughed islands amongst grass and fynbos shrubs on north and west facing slopes of low hills. Gasteria carinata var. carinata mostly occurs nearby and a small form of Haworthia maraisii is on an adjacent hill to the east. Haworthia hammeri grows in a rather clayey soil often amongst white quartzite pebbles. Gibbaeum austricolum shares the habitat at some of the populations. Haworthia hammeri occurs in four currently known localities in the Die Kop-Wydgeleë area.
Based upon leaf characters alone it can be rather difficult to place Haworthia hammeri in terms of closest relatives as it has the dull blue-grey colour and fuzzy facial lines as are found in Haworthia mutica while it shares the leaf-shape found in Haworthia badia. Although the plants are generally a bit smaller than Haworthia badia, the closest connection seems to be with the latter as the flowers are also very similar although, like the plants themselves, slightly smaller. The flowering time is during mid-summer (February) exactly the same time as that of Haworthia badia.The association with Haworthia badia is further strengthened by the fact that a normal spring-flowering Haworthia mutica can be found a mere 4 km to the west of Haworthia hammeri. The speculation that Haworthia hammeri resulted from an ancient hybridization between Haworthia mutica and a Haworthia mirabilis relative is plausible. One would then assume that the population eventually became isolated and the plants could establish themselves as a unique species.
An interesting feature worth mentioning is the fine ‘shark-skin’ epidermis texture found in Haworthia hammeri which is also found in Haworthia groenewaldii as well as the glabrous variant of Haworthia bobii growing 20 km to the south-east.
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