A new species of Stylosanthes (Leguminosae – Papilionoideae) from the Chapada das Mesas National Park in Maranhão, Brazil, is described. The new species, S. acicularis, was misidentified as S. angustifolia in the SLUI herbarium. It differs from S. angustifolia especially by inflorescence shape and rostrum length. The new species closely resembles S. hippocampoides by its small capitate inflorescences, absence of a rudimentary axis beneath the flower, only one inner bracteole, loments with only one fertile article and a very short rostrum, and the absence of a marginal vein and possession of up to five secondary veins in the leaflets. However, the two species differ by stem indumentum, bristle length, leaflet shape and venation, and shape of the outer bracteole margin. A morphological description, illustrations—including X-ray imaging of the leaflet venation—and notes on the geographical distribution, habitat, and conservation status of the new species are presented.

描述了巴西马拉尼昂州 Chapada das Mesas 国家公园的柱花草属（豆科 – 凤蝶亚科）的一个新种。新物种S. acicularis在 SLUI 植物标本室中被误认为是S. angustifolia 。它与S. angustifolia的不同之处尤其在于花序形状和花序长度。这个新物种与S. hippocampoides非常相似由于它的小头状花序，花下没有不发育的轴，只有一个内小苞片，只有一个能育物和一个非常短的喙的loments，并且没有边缘脉并且在小叶中拥有多达五个次脉. 然而，这两个物种在茎毛被、刚毛长度、小叶形状和脉络以及外小苞片边缘的形状方面有所不同。提供了形态学描述、插图（包括小叶脉络的 X 射线成像）以及关于新物种的地理分布、栖息地和保护状况的说明。