Since 1984 I have recorded all flowering plant taxa along a five-mile canyon route that climbs 4158 ft (1267 m) to the summit of Mount Kimball in the Santa Catalina Mountains of southern Arizona. In this flora of vascular plants in the Finger Rock Canyon Watershed, I describe the study area and its six vegetative associations, then discuss the impacts of drought, non-native species, and fire. The annotated flora, primarily based on data collected through 2017, includes information on abundance, distribution, vegetative associations, elevation where found, and months and years blooming. To investigate the effect of elevation on species richness and flowering duration, I divided the trail into five segments, approximately one mile (1.6 km) in length, and have focused primarily on an area about 30 ft (9.1 m) on either side of the trail. The phenological data collected is summarized for each taxon seen flowering from 1984-2017. The flora currently includes 615 specific and infraspecific taxa in 363 genera and 84 families. Although the watershed includes only about 0.6% of the area of the Santa Catalina Mountains, approximately 45% of the known flora of the range has been found here. This is particularly remarkable considering the area I have surveyed on foot is only about 7% of the watershed and less than 0.06% of the entire range.

A large population of the fully mycoheterotrophic orchid, Corallorhiza striata var. vreelandii, was monitored for nine years, 2009—2017, in the Santa Catalina Mountains of southeastern Arizona. High elevation slopes were chosen for an unusually high density of plants. Orchid stems were counted annually, and the number of flowering stems steadily decreased by 78% during the first seven years (2009–2015) in drought conditions. Following a partial return to average rainfall on the seventh through ninth years, the number of stems dramatically rebounded on the eighth and ninth years. Overall the total number of flowering stems decreased by 35% during the study. Precipitation from the previous winter and summer strongly correlated with the number of flowering stems observed. Years of extreme drought, with less than half of annual averages, resulted in a decline of flowering stems for two consecutive years, even when the following year had average rainfall. Two years of near average rainfall resulted in an increase on the second year. Orchid numbers were observed to fluctuate as its endophyte was dynamically affected by changes in annual precipitation. This study highlights the need for research on the impact of drought to ectomycorrhizal fungi and affiliated plant species.

Portions of the eastern Mojave Desert region of southeastern California, southern Nevada, and west-central Arizona that receive significant inputs of warm-season precipitation contain large areas dominated by various C4 perennial grasses including Pleuraphis rigida, P. jamesii, Bouteloua eriopoda, and B. gracilis. The lower elevation at which the two Bouteloua species occur rises from east to west in response to diminished precipitation, especially that received during the warm season. Unpredictability of warm-season precipitation also increases from east to west, but these grasses occasionally make use of cool-season precipitation stored in the soil, once temperatures required for the C4 photosynthetic pathway are achieved in late spring, but before the onset of summer monsoonal precipitation. Species distributions vary with elevation, with P. rigida occurring at lower elevations, B. eriopoda and P. jamesii at intermediate elevations, and B. gracilis at higher elevations. Composition of communities containing the latter three species is similar to grassland formations of the cool-temperate grasslands (grama-galleta steppe) of the Colorado Plateau region. Small, less predictable amounts of warm-season precipitation probably impose the greatest limitation to the diversity of C4 grasses in the eastern Mojave Desert region. However, due to warmer minimum winter temperatures, the woody plant and succulent floras associated with perennial grasses in the eastern Mojave region bear greater resemblance to those of the warm-temperate, semi-desert grasslands of west-central Arizona, southeastern Arizona, and the Sonoran and Mojave Deserts. The presence of these woody plant and succulents in perennial grass-dominated communities in the eastern Mojave Desert imparts a structural character similar to that of the warm-temperate semi-arid grasslands of southern Arizona. Although climate (particularly warm-season precipitation) is a first-order determinant of the occurrence of perennial C4 grasses in the eastern Mojave Desert region, geological characteristics that control soil formation and soil hydrological behavior strongly influence composition of communities. The common denominator of sites dominated by grasses is a soil with relatively thick, fine-grained soil horizons that are conducive to exploitation by relatively shallow, diffuse, fibrous root systems of those grasses. Such soils occur in diverse settings, ranging from relatively steep hillslopes underlain by bedrock to gently inclined alluvial fans. In rocky hillslope environments, these kinds of soils are associated with late Pleistocene colluvium deposits in which eolian dust accumulation is principally responsible for forming the thick, fine-grained horizons. Erosion of these soils on hillslopes contributes to hydrological conditions more conducive to taproot systems of woody plants that occupy deeper fractures and joints in bedrock. Similarly, erosional truncation of well-developed soils of alluvial fans and exposure of cemented, relatively impenetrable calcic horizons produce a shift in dominance by perennial grasses to woody plants. In many settings, the presence of relatively dense perennial grass cover plays an essential role in moderating surface flows and inhibiting erosion. Prior to Anglo-American settlement of the region in the late 1800s, occasional wildfires may have fostered dominance of perennial grasses in some of these areas. Since the 1890s, livestock ranching has significantly impacted perennial grass-dominated vegetation. Removal of livestock from portions of the region around 2000, coupled with years of abundant warm-season precipitation, in some cases combined with wildfire, has led to a resurgence of perennial grasses in some areas. Effective management and conservation of these areas require a comprehensive understanding of the composition, occurrence, and ecological functioning of these communities.

Ragged Top is a small desert peak in north-central Pima County, in the Santa Cruz River watershed in the northeastern Sonoran Desert. There are 398 plant taxa in 66 families, on Ragged Top and in the immediate watershed. Ragged Top's rugged topography and its geographic position in relationship to other biotic communities in the region have made it a habitat for a remarkable palette of plants. One species, Pisonia capitata (Nyctaginaceae), was an addition to the flora of the United States, and another, Bouteloua diversispicula (Poaceae), was a confirmation of a single, questionable United States collection from 1867. This is a study of the vascular plants and the vegetational composition on the mountain and surrounding desert.