Bulb ovoid, 1.5-2.5 × 1-1.5 cm with outer tunics membranaceous, brown, the inner ones whitish. Leaves 7-8, glaucous, 4-6 cm long, 1-1.5 mm wide, flat in the adaxial face, convex and ribbed in the abaxial one, convolute and prostrate at maturity. Stems solitary or paired, 4-10 cm tall, erect to procumbent. Pedicels 3-8 mm long. Raceme 1-3 cm long, provided with 4-12 flowers. Perigone stellate, 3.5-4 mm in diameter. Tepals white-liliaceous to liliaceous, with mibrid violet, outer ones ovate, acute at the apex, 4-4.3 × 2.3-2.5 mm, inner ones oblong, rounded at apex, 3.5-4 × 1.7-2 mm. Stamens equal, 3-3.4 mm long, filaments white below and liliaceous above, anthers dark violet, 1.2-1.3 mm long. Ovary white, obpyriform, 2 × 1.7 mm. Style liliaceous, 1.4-1.5 mm long, with stigma papillose. Capsule subglobose, dark green-glaucous, maculate with purple, 3.5 mm in diameter.
P. hierae was exclusively found at Marettimo (Egadi Archipelago, W Sicily)
it grows on rocky stands very close to the sea. This small geophyte is quite rare on the island and it colonizes Mesozoic limestone characterized by small hollows covered by a feeble layer of soil. It is a member of ephemeral sub-halophilous communities characterized by rare or very specialized therophytes such as Senecio incrassatus Guss., Hymenolobus revelieri (JORD.) BRULLO subsp. sommieri (PAMP.) BRULLO, Sagina maritima G. DoN, Silene sedoides PoiRET, Bellis annua L., Catapodium balearicum (WILLK.) SCHOLZ, Parapholis incurva (L.) HUBBARD, etc.
P. hierae, due to its small size, is quite well differentiated from the other species belonging to the genus Prospero, but for some morphological features, such as few-flowered inflorescence, small flowers, and narrow leaves, it seems to be more related toP. corsicum (BOULLU) J. M. TISON from Corse and Sardinia, P. pulchellum (MUNBY) SPETA from N. Africa, and P. minimum SPETA from Crete. In particular, P. corsicum differs from P. hierae in having smaller bulbs, flowers, pedicels, tepals, ovary, stamens and capsule, as well as shorter, green, subcylindrical leaves. As concerns P. pulchellum, it is differentiated by few, green, narrower leaves, smaller tepals, stamens and ovary. Finally, P. minimum is characterized by smaller bulbs, ovary and capsule, longer, narrower and subcylindrical leaves, pink and larger tepals. Besides, P. hierae is well differentiated from the other Sicilian populations probably referable to P. autumnale s. 1. In order to highlight the morphological relationships between these species, an iconography of a diploid population with 2n = 14, coming from Trapani (W Sicily) and belonging to P. autumnales s. 1., is provided. According to literature (KER-GAWLER 1806, STEINHEIL 1834, BAKER 1873, MAIRE 1958, SPETA 1982, 1998, CONTANDRIOPOULOS & ZEVACO-SCHMITZ 1989), the typical populations of P. autumnale s. str. are characterized by big bulbs, leaves green, numerous, filiform, up to 35 cm long, stems erect, up to 35 cm long, inflorescence loose and many flowered, tepals 4.5-5 mm long, capsule obovoid. As concerns its typification, we agree with SPETA 1982 that proposed as lectotype the original iconography of ,Hyacinthus autumnalis minor" published by CLUSIUN 1601 and afterwards quoted by LINNE 1753 in his protologue as synonym of Scilla autumnalis. Since this is a rough illustration, according to the art. 9.7 of ICBN (McNEILL & al., 2006) it would be desirable to designate an epitype which should be chosen among tetraploid Spanish populations of P. autumnale s. str.
Due to its very peculiar ecological requirement and its punctiform distribution, as well as for some morphological features, P. hierae is probably derived from a detached population of Prospero autumnalis that likely got isolated as a consequence of the colonization of extremely specialized and geographically isolated habitats.