Flora of New Zealand Series

Placodium illitum Knight, Trans. Linn. Soc. Lond. ser. 2, Bot. 1: 282 (1877).

Lectotype: New Zealand. Sine loco. Charles Knight, H-NYL 23848!

Thallus ± determinate, lobate at margins, orbicular to spreading, 1-3(-5) cm diam., with a well-defined, brown-black, marginal prothallus, saxicolous. Lobes minute, folded, confluent. Upper surface continuous, minutely and irregularly cracked, not areolate, cracks very fine (×10 lens), smooth, glaucous, whitish or creamish, matt, epruinose, without isidia or soredia. Cephalodia scattered, flattened, rounded, sessile, 2-3 mm diam., radially wrinkled, folded-effigurate, somewhat cracked, yellow-pink, matt. Apothecia sessile, rounded, to 3 mm diam., thalline margin prominent, entire or subcrenulate, matt, disc plane, dark brown to brown-black, matt, epruinose. Hymenium 80-140 µm tall, yellowish above. Ascospores biseriate, ellipsoid, 12-18 × 6-9 µm. Chemistry: Cortex K-, C+ rose; medulla K- or + pale yellow, C+ rose, Pd-.

N: Wellington (Tararua Ra.). S: Nelson to Fiordland. St: A: On stones and rocks in stream beds or damp banks and shingle slides, subalpine to alpine, most common in glaciated areas, close to and west of the Main Divide.

Endemic

P. illita is characterised by the well-developed marginal prothallus and the brown-black, epruinose apothecial discs.