Sporisorium rarum R.G.Shivas, A.R.McTaggart & Vánky

Description

Sori in all spikelets of an inflorescence, occupying the inner floral organs, ovoid to ellipsoidal, 1.0–2.5 mm long, 1.0–1.5 mm wide, often with remnants of floral envelopes as short acute distal tips, partly hidden by the outer floral envelopes and covered by a greyish brown peridium. Sori may occupy 2–several of the distal spikelets, then irregularly lobed, up to 9 mm long and 2 mm wide. Peridium rupturing from its apex at maturity, sometimes by a longitudinal split, exposing the blackish brown semi-agglutinated to powdery mass of spore balls, spores and sterile cells surrounding a simple stout tapering columella c. the length of the sorus.

Spore balls 40–125 µm long, composed of tens to hundreds of loosely connected spores that readily separate.

Spores when mature solitary, globose or ellipsoidal to subpolyhedrally irregular, 7.0–9.5 × 6.5–9.0 µm, yellowish brown; wall uniformly c. 0.5 µm thick; in LM finely and moderately densely punctate-verruculose; spore profile smooth, in SEM moderately densely low-echinulate, between the spines densely and minutely verruculose.

Sterile cells solitary, in pairs or in small irregular persistent groups; individual cells globose, ellipsoidal or irregular, rounded on the free surface, flattened on the contact surfaces, 6–16 (–20) µm long, hyaline to yellow-tinted, with a few oil droplets in each cell; wall 0.8–1.5 µm thick, smooth.

Hosts
   
Host family: Poaceae
   
Host species: Eulalia aurea (Bory) Kunth

Distribution

States & Territories: NT

Comments

Sporisorium rarum and S. eulaliae are the only smut species recorded from Eulalia in Australia (Vánky, 2000). The former has much smaller spores than S. eulaliae (9.5–15.0 × 8–12 µm). It is most similar to S. guangxiense L.Guo, which occurs on Eulalia pallens (Hack.) Kuntze in China. The spores of S. rarum are larger, more regular, and have thinner and more uniform spore walls than those of S. guangxiense, which are variable in shape and size, 4–7 (–8) × 5.5–9.0 µm, with an unevenly thick spore wall of 0.5–1.0 (–1.5) µm.