Abstract. DELFORGE, P. - Contribution to the knowledge of the Orchids of the island of Kythera (Attica, Greece). [Natural. belges 91 (Orchid. 23) (2010): 47-205]. After a presentation of the tectonics, the geology, the geomorphology, the vegetation, the history, and the human impact on the landscape of the island of Kythera, a review of the past and present studies and research about its orchids is made. It appears that 45 orchids species were known for Kythera before 2010 (Table 1). Research in Kythera in March and April 2010 has revealed 48 orchid species for the island, bringing their number up to 51 (Table 1). Among the 51 species known at the present for the island, 1 is doubtful and/or probably extinct (Ophrys ulyssea), 2, not seen in 2010, are sporadic or extinct (O. argolica and O. omegaifera), and 2 are represented in 2010 by only 1-2 individuals (Ophrys cerastes, O. spruneri). One species, Paludorchis laxifora, is represented by only one population, and 3 other species are present in only 2/296 squares of 1 km x 1 km: Ophrys calocaerina, O. kedra, and O. lutea. A discussion is made for each species observed or listed in the island of Kythera, following the order used in DELFORGE (2006A, 2010).

Limodorum abortivum is very local, Spiranthes spiralis, which flowers only in Octobre, is extremely local (first mention for Kythera). The genus Dactylorhiza is represented only by D. romana (extremely local).

The genus Serapias is species-rich in the island and comprises 7 species and numerous hybrids. (1) S. parviflora is rather widespread, (2) S. politisii extremely local, (3) S. bergonii local, (4) S. vomeracea very local, (5) S. orientalis rather widespread, with 2 varieties: var. orientalis and var. sennii, (6) S. cordigera very local, and (7) S. lingua very local.

Most of the Anacamptis pyramidalis seen in 2010 belong to A. pyramidalis var. brachystachys, rather widespread, and another variety, probably endemic, is described here as A. pyramidalis var. cerigensis P. DELFORGE.

The former genus Orchis s.l. is represented by 9 species belonging to 6 genus, Paludorchis with (1) P. laxiflora (extremely local, only one population probably endangered); Vermeulenia with (2) V. papilionacea var. aegaea (widespread, with 2 quite different waves of flowering); Anteriorchis with (3) A. fragrans (rather widespread); Orchis s. str. with (4) O. quadripunctata (local), (5) O. italica (very widespread, the most widespread orchid species in Kythera), and (6) O. anthropophora (very local), Neotinea with (7) N. lactea (extremely local), (8) N. tridentata (rather widespread), and (9) N. maculata (very local, but frequency probably underestimated).

The genus Himantoglossum is represented only by H. robertianum (rather widespread).

The genus Ophrys is represented by 30 species in Kythera.

The sectio Pseudophrys GODFFRY comprises 14 species in the island which belong to 5 species groups: the Ophrys iricolor group with (1) O. iricolor (local) and (2) O. cf. mesaritica (extremely local); the O. funerea group with (3) O. perpusilla (very local, first mention for Kythera), (4) O. leucadica (very local), and (5) O. creberrima (very local, first mention for Kythera); the O. attaviria group with (6) O. parosica var. parosica (very local), (7) O. kedra (extremely local, first mention published for Kythera, first mention outside Crete), (8) O. cinereophila (very local), and (9) O. calocaerina (extremely local); the O. lutea group with (10) O. sicula (rather widespread), (11) O. phryganae (rather widespread), and (12) O. lutea (extremely local); the O. omegaifera group with (13) O. omegaifera (extremely local, not seen since 1957, probably extinct) and (14) O. sitiaca s. str. (very local, first mention for Kythera).

The section Ophrys (= Euophrys GODFERY nom. nudum) in Kythera comprises 16 species which belong to 7 species groups: the O. tenthredinifera group with (1) O. bombyliflora (very local, great majority of small flowered plants and 4 small populations of plants with large flowers), (2) the large-flowered O. leochroma (very local, first mention for Kythera), (3) O. villosa (rather widespread, very small flowered), and (4) O. ulyssea (doubtful, not seen in 2010); the Ophrys apifera group with (5) O. apifera (extremely local, main population endangered); the O. bornmuelleri group with (6) O. cytherea (B. BACMANN & Il. BAUMANN) P. DELFORGE comb. et stat. nov. (very local, probably endemic); the O. oestrifera group with (7) O. cerastes (extremely local, only 1 individual seen in 2010) and (8) O. ceto (very local); the O. heldreichii group with (9) O. calypsus [rather widespread, with 3 varieties: var. calypsus (rare), var. scolopaxoides (rare) and var. pseudoapulica (rather widespread, = O. episcopalis auctorum non POIRET, = O. holoserica subsp. cerigona B. BAUMANN & H. BAUMANN)]; the O. reinholdii group with (10) O. reinholdii (very local) and (11) O. ariadnae (very local); the O. argolica group with (12) O. argolica (not seen in 2010, sporadic or extinct); the O. mammosa group with (13) O. ferrum-equinum (rather widespread, with not very varied flowers: majority of f. ferrum-equinum and some individuals of f. subtriloba, f. minor, and f. labiosa), (14) O. spruneri (extremely local, only 2 individuals seen in 2010), (15) O. mammosa (extremely local), and (16) O. herae (very local).

Viewed in the way of the orchid biogeography, the orchid flora of Kythera here presented seems to indicate influences almost egal from the Peloponnesus and from the Cardaegean zone (i.e. Crete, Karpathos, and the Cyclades).

After carefull examination of the literature, it appears that some old or recent mentions of orchids, made for Kythera, are questionable or erroneous. As a result, the following species must be deleted from the list of the orchids of K ythera: Anteriorchis (Orchis) coriophora (s. str.), Ophrys aranifera (= O. sphegodes), O. bremifera, O. candica, O. cornuta, O. cretica, O. episcopalis, O. 'fuciflora-holoserica', O. fusca (s. str.), O. heldreichii, O. (holoserica subsp. vel var.) maxima, O. oestrifera, O. pseudommamosa, O. scolopax, O. tenthredinifera (s. str.).

A list of 51 species and 11 hybrids, and 61 distribution maps, based on the presence in 296 UTMwgs84 squares of 1 km x 1 km, are provided as well as a list of 553 sites prospected during the spring 2010, from March 15 to April 23.

Ke-Words: Flora of Greeee, flora of Aegean, flora of Kythera; Orchidaeeae, A. pyramidalis var. cerigensis P. DELFORGE var. nova, Ophrys cytherea (B. BAUMANN & H. BAUMANN) P. DELFORGE comb et stat. nov.