The study area is illustrated in Figure 1 with emphasis on water courses that riparian mesquites can follow. The compositions of the 3 sites are made clear in Figures 2 & 3. Hermosillo Group 1 is tall old trees that have 1 PR only like Navajoa, whereas the other trees of 2-4 m including Mazatán & El Novillo are infiltrated by velutine derivatives from the north since they carry 2 PR. Navajoa with old trees > 10 m has Torreyana trees of 1 PR only.

Guaymas begins with a new element, the 24 mm rachis (24 LR) of the new race Tiny of 1 PR only, that is not known elsewhere. The intermediates formed by Tiny times torreyana are infiltrated slightly by 2 PR (Group 7). The few torreyana trees of Guaymas (Group 8), < 4 m tall typify the former occupants of the Hermosillo—Guaymas area, many having been > 10 m tall in former times. Fluctuations in LR & LP as well as in the other foliar variables with consequent high variance are common in most algarroban mesquites. These distributions lie between uniform and normal.