Dendrobium petrophilum (Kraenzl.) Garay ex N.Hallé

Pignal, Marc, Laudereau, Christian, Gâteblé, Gildas & Laudereau, Pierre-Louis, 2022, Dendrobium petrophilum (Kraenzl.) Garay ex N. Hallé, a well-named species describing its unusual chasmophytic ecology, Adansonia (3) 44 (1), pp. 1-9 : 4-6

Dendrobium petrophilum (Kraenzl.) Garay ex N.Hallé

( Figs 1 ; 2 A-D; 3 A-E; 4 )

Flore de la Nouvelle-Calédonie et Dépendances 8: 150 ( Hallé 1977). — Eria petrophila Kraenzl., Vierteljahrsschrift der Naturforschenden Gesellschaft in Zürich 74: 90 ( Kränzlin 1929). — Tetrodon petrophilus (Kraenzl.) M.A.Clem. & D.L.Jones , Orchadian 12: 311 ( Clements & Jones 1998).

— Type: New Caledonia. In Felsritzen am Sommet Arama , auf Schiefer c. 400 m ü. M. [rock cleft at the Arama summit, on schist c. 400 m], fl., 16.IV.1925. A.U. Däniker 2904 (holo-, Z [ Z-000016414 ] image seen.).

ADDITIONAL MATERIAL EXAMINED. — Province Nord: Poum, fente de rocher au sommet Arama , 400 m, 16.IV.1925, A.U. Däniker 1904, P [ P02106269 ] photocopy of the type with an additional drawing of the flower by L.A. Garay!. — Poum, Golone , 88 m, végétation basse, schiste dégradé, 16.V.2020, D. Fleurot et P. Dayé 714 ( NOU [- NOU091019 ]!). — Poum, Niap ( Mts Ninndo ), 214 m, maquis très ouvert, crête de schiste siliceux érodé, 25.VII.2020, D. Fleurot 763 ( NOU [ NOU091249 ]!). — Poum, Vache Crevée , 158 m, maquis très ouvert, crête de schiste siliceux érodé, 14.XI.2020, D. Fleurot 796 ( NOU [ NOU091248 ]!). — Poum, Arama , 25.X.2018, C. Laudereau 1173, NOU [ NOU091351 ]!. — Poum, Arama , 13.IX.2019, C. Laudereau 1294 ( NOU [ NOU091402 ]!; P!). — Poum, Arama : Mts. Ninndo , 22.VI.1972, H.S. MacKee 25584 ( P [ P00115081 ]!). — Poum, Col d’Arama , 6.VI.2019, H. Vandrot et J. Girardi 1508, NOU [ NOU106730 ]!.

ETYMOLOGY. — The epithet refers to the words “petros” in Greek which refers to rock and “philus” which refers to like, appreciate.

PHENOLOGY. — From herbarium specimens, flowers have been recorded from April through November (except in August) and fruits have been recorded all the year.

ECOLOGY. — The epithet is very well fitting the ecology of this species usually living on rocks (saxicolous) and especially the cracks of the rocks (chasmophyte), Fig. 2C . However, Dendrobium petrophilum is also able to grow at the base of trees and shrubs (but not truly epiphytic, Fig. 2D ) where it can get some shelter from the harsh natural environmental conditions (extreme drought, strong prevailing wind, full sun, rocks with no or little soil) encountered in this type of “acidic maquis” ( Fig. 2A ) which is very different from the typical New Caledonian “ultramafic maquis”. The bedrock is a siliceous schist and its derived soil (if any) is a kind of ferric acrisol ( Latham 1975). Some other species like Codia microphylla Vieill. ex Guillaumin , Homalium buxifolium Däniker , Leichhardtia oubatchensis , Phyllanthus golonensis M.Schmid and Tristaniopsis ninndoensis J.W.Dawson are well adapted to this type of maquis.

CONSERVATION STATUS. — A first IUCN assessment was made on 29 January 2016 by the local Red List Authority (RLA Endemia) which proposed the species as Data Deficient (DD) because of too much taxonomic uncertainty. This assessment has been published in 2020 on the IUCN Red List Portal ( Butin et al. 2020a). Since, the species has been rediscovered in 2018 in the type locality (locus classicus) by two of the authors of this note, and in other places by other people, since then, we have been able to clarify its taxonomic status. A second IUCN assessment by the RLA Endemia took place on 20 November 2020 and proposed the species as EN B1 ab(iii,v)+2ab(iii,v). We fully agree with this proposed status because of the very high fire threat. According to some observations (D. Fleurot pers. comm.), after a rapid fire event, the pseudobulbs are drying out and can be observed several years after the event ( Fig. 2D ). In addition, the species is protected in the Province Nord ( Northern province ).

DESCRIPTION

Saxicolous plant of (17-)26-34(-39) cm. Pseudobulbs bifoliate, ovoid, tubular to conical, (23-)32-40(-74) × (4-)6-8(-13) mm, with 3 internodes, bright orange on ageing organs and on dry specimens, covered with 3 deciduous, large papyraceous, translucent and 7-veined cataphylls applied to the pseudobulb. Leaves: gutter-shaped pseudopetiole canaliculate, 3 mm long, blade (19-)26-41(-58) × (6-)8-10(-12) mm, obovate to elliptic oblong, apex obtuse, asymetrical. Inflorescence subterminal, (70-)260-320(-380) × 1 mm, erect, slender and multiflorous, flower non resupinate, sometimes with a ramification, (9-)10-13(-21) flowers. Flower: Peduncle (5-)6- 8(-9) × 0.6-1 mm, white. Tepals greenish-yellow. Median sepal lanceolate, (4.9-)5.4-6.3(-6.8) × (1.4-)1.5-2.7(-5.1) mm. Lateral sepals triangular falciform, (5.1-)6-6.5(-8) × (1.6-)1.7-2(- 2.4) mm. Petals spatulate, (4.7-)5.3-6.2(- 6.5) × (1.4-)1.5-1.8(-1.9) mm, slightly deflected. Lip, 5.1 × 2.8 mm, 3-lobed. Hypochile and mesochile thick with a gibbous callus, white, obscurely tricarinate, the keels extended by 3 flattened, slightly divergent extensions, pink, 1 mm long and 0.7 mm wide (median extension), 0.4 mm wide (lateral extensions). Lateral lobes oriented upward, 2.5 × 0.9 mm, light pink striped with dark pink, roughly trilobular, the proximal lobule, small, rounded, 0.44-0.47 wide, the median lobule, ovate, 1.4 × 0.8 mm, the distal lobule, triangular, 0.8 × 0.4 mm, ending in a white tip. Median lobe trilobulate, 2.4 × 2.9 mm, white, lateral lobules, triangular, non-deflected, 0.8 × 0.7 mm, greenish-white, median lobule rounded, 2.3 × 2 mm, white, obscurely carinate. Column white, except the edge of the stigma which is pinkish, 4.5 × 1.3 mm with a 2 mm long mentum, and 1.5 mm deep at the point of attachment to the ovary. Androecium: anther cap (connective appendage), white, 0.6 mm wide and 0.6 mm high, pollinia, 2, yellow, obovoid, 0.5 × 0.2 mm. Gynoecium: stigma rectangular, 0.9 mm wide and 0.6 mm high, ovary, 2-3 × 0.9 mm, reddish. Fruit obovoid to spherical, 13-15(-17) × (7-) 8-10 mm, greenish with purple strips.

NOTES

In 1972, H.S. MacKee collected a sterile orchid at Arama (MacKee 25584, Monts Ninndo, P00115081) and apparently sent some pseudobulbs of it to P for greenhouse cultivation, presumably because MacKee was thinking this orchid was interesting and worthwhile further ex situ examination and flowering. At P, the first author did not find any record of its cultivation and flowering in the archives of Service des Cultures. Hallé (1974, mss. in herb) identified this specimen as D. multilobatum Guillaumin and later, synonymized this name under D. oppositifolium in his New Caledonian flora of Orchidaceae ( Hallé 1977: 122) . Another interesting and related specimen (MacKee 21630) was collected fertile in 1970 and a plant was sent to Paris Museum greenhouses where it flowered on 30 May 1974. Hallé collected the inflorescence of it at P and added it to the original specimen (P00115083). Because the original specimen was also initially determined as D. multilobatum by Hallé, we have checked in detail the flowers of the cultivated specimen (that are slightly smaller than the ones of the in situ plant) to confirm labels of MacKee 21630 and 25584 have not been mixed in P greenhouses. We conclude both the in situ and ex situ flowers belong to D. oppositifolium so labels were most probably not mixed. It is to be noted that many New Caledonian orchids and particularly Dendrobium have been exported to P and other Europeans institutions and nurseries for ex situ cultivation ( Gâteblé 2015: 24-27, 294).

Figures

FIG. 1. — Drawing of the type of E. petrophila Kraenzl. by L.A. Garay completing the photocopy of the type kept at Z.

FIG. 2. — Dendrobium petrophilum (A-D) habitat, ecology and threat compared to D. oppositifolium (E) habitat: A, the type locality at Arama pass crest; B, three plants (arrows) at the Arama pass siliceous crest exposed to full sun and prevailing wind;C, typical chasmetophytic microhabitat within the cracks of the siliceous rocks; D, anthropogenic fire threat showing a burnt colony at the base of a dead burnt trunk of the microendemic Tristaniopsis ninndoensis J.W.Dawson; E, epiphytic habit in a high altitude (c. 1200 m) and open canopy montane forest at Mont Panié. A, Arama pass, 27.VIII.2019; B, Arama pass, 30.IX.2018; C, D, Vache Crevée, 14.XI.2020; E, Mont Panié (Pwé Taao), 31.V.2014. Photos from: A, B, E, G. Gâteblé; C, D, D. Fleurot.

FIG. 3. — Comparison of the flowers of Dendrobium petrophilum (Kraenzl.) Garay ex N.Hallé (A-E) and D. oppositifolium (Kraenzl.) N.Hallé (F-J): A, flower (front side); B, column, profile side (p) and front side (f); C, column and lip, profile side; D, lip, ventral side; E, lip spread out, ventral side (f) and backside (d); Dendrobium oppositifolium: F, flower (front side); G, column, profile side (p) and front side (f); H, column and lip, profile side; I, lip, ventral side (f) and backside (d); J, lip, ventral side (f). Photographs of D. petrophilum are from expeditions at Arama (Northern province), photos C. Laudereau.Photographs of D. oppositifolium, Plateau de Dogny, photos C. Laudereau. Olympus EM1MarkII, 30.V.2020, combined as a board. Scale bars: A, 3 mm; B-E, G-J, 5 mm; F, 4 mm.

FIG. 4. — Distribution of Dendrobium oppositifolium (Kraenzl.) N.Hallé (blue) and D. petrophilum (Kraenzl.) Garay ex N.Hallé (red) in New Caledonia (La Grande Terre and Île des Pins):A, focus in the Poum area.Grey shaded areas represent ultramafic outcrops. Circles correspond to herbarium specimens while squares correspond to in situ observations from various authors and compiled by Endemia.nc.Tm, To and Tp represent respectively the type localities of D. multilobatum Guillaumin, D. oppositifolium and D. petrophilum names.