Two  types  of  sites  are  typical  for  this  species.  One,  along  the  coast  in  "huayco"  (flash  flood) situations from 50 to 700 m in soils that are sandy loam or clay in texture. The other more common location  is  roadsides,  mountain  slopes,  and  washes  (up  to  1600  m)  that  drain  into  valleys  of  the Pacific watersheds. The latter sites are sandy to stony with rocks normally present. Most sites are extremely or very dry -- a striking feature now being exploited in a drought-tolerance improvement program (Rick, unpublished). The most common associate of S. pennellii is Loaza spp., particularly between 500 and 1200 m elevation; in fact, these Loaza spp. are so consistent as indicator plants that they have seldom failed to lead to useful seed collection of S. pennellii. Columnar cacti are common from 600-1000 m in the northern part of the distribution from Chicama to Chillon. An unidentified yellow-flowered legume is the  characteristic  companion  plant.  Another  association  to  be  verified  is  a  Mirabilis-like  species (Nyctaginaceae) mentioned twice in collections north of Huaura. Sympatry with  L. peruvianum has been recorded several times from Huaura to Pisco, 500-1600 m. L. hirsutum has been found only at Espíritu  Santa  (Lurín  watershed).  The  only  instance  of  S.  pennellii  as  the  dominant  vegetation element is Sayan-Churín (DHUNA 1001, 1013), where it was observed on a mountainside after the rainy  season  of  1972.  L.  pimpinellifolium  was  also  present  here  in  the  lower  slopes  above  the irrigation ditches and close to the pennellii plants. II. DESCRIPTION OF THE COLLECTIONS ARRANGED BY WATERSHEDS AND LOMAS 1. Watersheds: Tumbes, Chira, and Piura (Table 5, fig. 2) The  two  northernmost  watersheds  on  the  coast  of  Perú  (Tumbes  and  Chira)  have  their  origins  in Ecuador. They belong to the zone of transition to tropical conditions and the rivers have water the year around. The Tumbes watershed has not been well collected with regards to Lycopersicon spp. As shown in Table 5, only one herbarium specimen, L.  peruvianum,  is included Expedition for 1974 in western South America) collected accessions of the red-fruited L. pimpinellifolium from this area. Since there is a planned  project  for  irrigation  and  development  of  the  Puyango  (Ecuador)-Tumbes  (Perú)  area  during l976-1986, there is danger of major disturbance of this natural habitat. The Chira watershed is one of the largest of the Peruvian coast if the tropical area that corresponds to  Ecuador  is  included.  Like  Tumbes,  it  also  has  a  year-around  water  supply  and  is  not  well  known floristically. The valley can be divided into 2 basic areas: a) a desert coast delta (0-300 m) with a very narrow (2-4 kms on each side) vegetation strip along the river which is dedicated to irrigated farming (Pima  cotton,  citrus,  coconuts,  rice,  bananas);  and  b)  a  transition  zone  from  dry  through  annual intermittent rain flora to tropical southern Ecuador conditions where cattle grazing is the most common activity. This area ranges from 300 to 2500 m. The Piura river basin can be divided into two distinct zones: a) the desert zone, where the river flows west from Chulucanas for approximately 150 km; and b) the mountain zone starting in the Chulucanas- Morropon area at 500-1000 m and ending in Huarmaca at 2500 m. This valley has an intermittent water supply based on varied rainfall that occurs between December and April. While the mountain zone gets yearly rains, the desert has fewer rainy years but these usually produce  a  very  profuse  annual  flora  that  can  support  cattle  for  2  to  3  dry  years.  The  river  dries  up usually around the Chulucanas area; but at the Quebrada de San Francisco, water from the Quiroz river (Chira basin) was diverted into the Piura in 1954. In 1976 another diversion from the Chira was finished. Thus, natural and farming conditions are changing, and it is possible that the area below the continuous water source now has a mixed vegetation from the two basins. The main crops in the middle and lower sections  are  long-staple  cotton,  corn  and  sorghum;  and  in  the  higher  watershed,  rice,  cotton,  fruits (mango, citrus, avocado) and coffee. This is the only coastal valley where cattle can be raised on pastures based on the intermittent desert vegetation.

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