Robust perennial herbs 7-10 dm tall, strongly rhizomatous and bulbous-based, the bulbs ovoid, thick-scaled, at ends of short, scaly, ascending or horizontal rhizomes. Principal leaves stiff, subdistichous (the lower ones transitional to bulb scales and mostly sheath), erect to slightly ascending, twisted, 30-50 cm long, longer than the scape sheaths; sheaths (and bulb scales) ecarinate, scabridulous, ciliate or ciliolate at dilated base, sordidly purple-brown, multicostate, abruptly dilated below, then gradually narrowed in to blade, eligulate; blades compressed, linear, slightly twisted, 3 - 4 times longer than sheaths, l ongitudinally distinctly few-nerved, the tips asymmetrically subulate; margins thickened, entire, commonly with median sulcus. Scape sheaths firm, twisted, shorter than leaves. Scapes straight or flexuous, twisted, terete toward apex, ca. 1 mm thick, finely striate. Spikes broadly to narrowly ovoid, 1.2-2 mm long, short-attenuate, blunt or obtuse, several-flowered, the sterile bracts several, the lowermost pair oblong-lanceolate, ca. 5 mm long, blunt with linear dorsal areas, the inner ones broader, gradually longer, grading evenly into the fertile; fertile bracts broadly obovate, 8 -8.5 mm long, ecarinate, broadly convex, broadly rounded, entire becoming erose, the dorsal areas elliptic, greenish brown, with indistinct median costae. Lateral sepals free, strongly inequilateral, broadly spathulate, 7-7.5 mm long; carinal keel broad, irregularly ciliolate. Petal blades broadly obovate to suborbicular, 6mm long, yellow, dentate. Staminodia bibrachiate, the branches densely long-penicillate. Anthers curved-oblong, 2- 2.5 mm long, emarginate and deeply sagittate, the filaments stout, c a. 0.5-1 mm long. Capsule obovoid, ca. 3.5 -4 mm long, the placentation basal. Seeds numerous on long funicles, broadly ellipsoid, apiculate, 0.4 -0.5 mm long, shiny, deep brown, longitudinally distinctly multicostate.
Thus far known only from wet savanna at low elevation (200 m), Santa Cruz Province, Bolivia.
In existing treatments for Xyris of South America this species appears to stand apart, perhaps the nearest to it being X. nilssonii Malme, a species that extends from the western planalto of Brazil westward in to Bolivia. However, that species, while bulbous-based, definitely lacks the stout scaly rhizomes that connect the larger, more nerved, bulbs of X. boliviana. Xyris boliviana is more robust, darker-based. Its leaves in venation and margin are similar, but the sheath bases are ciliate rather than entire, lacking the lustrous dark brown borders of X. nilssonii. The spikes of X. boliviana are similar in being attenuate-based, but are larger with more and broader fertile bracts, which are entire (rather than scarious-lacerate) and with less distinct narrower dorsal areas. The broadly spathulate lateral sepals are very inequilateral, rather than equilateral, are blunt rather than acute, and the seeds are slightly shorter, darker, more lustrous, and broader. In habit Xyris boliviana has some resemblance to X. asperula Martius, but that species is in an entirely different complex, since it has no dorsal areas, lacks attenuate spike base, and has longer lateral sepals. Since we have few records of xyrids from this particular part of Bolivia, and since the plant has been collected now from two different localities within the Parque Nacional, it is quite likely that further records of it will become available as the region becomes better known botanically.