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This study describes the structure and phenology of Sahelian rangelands during the rainy season. It was undertaken in thorny steppe on a grazed plot and a nearby fenced plot with otherwise similar site characteristics. Measurements were taken every 10 days over two rainy seasons between July and October 2022 and between August and October 2023. The measurements included the phenological stage, the vegetative and flowering height, the foliage cover, and the phytomass. The results showed that phytomass did not systematically differ between grazed and fenced plots. Flowering started as early as mid-July, but most of the plants flowered in early October. Flowering and fruiting occurred earlier (based on the number of days after the first rain) in the late rainy season (2023) than in the early one (2022). These stages reached their peak in October; senescence began in October. Vegetative height, reproductive height, and coverage were similar between the two years. Height peaks were similar, but they were reached earlier (based on the number of days after the first rain) in the late rainy season than in the early one. Coverage peaks were similar (59.8% in the early rainy season vs. 65.8% in the late one). Vegetative height (around 30 cm), reproductive height (around 36 cm), and coverage (around 60%) reached their maximum in October, but reproductive height was greater than vegetative height. These parameters were lower at the grazed, and flowering started earlier at the grazed site. Grazing reduced cover and height, and delayed flowering. Structure and phenology were more sensitive to changes in rainfall between years. Knowing phenology helps determine the best time to harvest the phytomass, because the nutritional quality of the forage is known to decrease after fruiting.