Orchid Information - Genus Dendrobium section Diplocaulobium subsection Mekynosepalum

KEY TO THE SPECIES OF DENDROBIUM SECTION DIPLOCAULOBIUM SUBSECTION MEKYNOSEPALUM
Based on the type descriptions

1a. Keels on the lip present on hypochile only, on epichile at most with more or less vague ridges == 2
1b. Keels on the lip present on both hypochile and epichile == 5

2a. Keels in basal half of hypochile low and narrow, in apical half high and plate-like; on basal 2/3rd of epichile with a linear¬lanceolate ridge (possibly minutely puberulent). Flowers small, less than 5 cm wide == Dendrobium wantipiense
2b. Hypochile keels not partly high and plate-like == 3

3a. Sepals c. 3.2 cm long == Dendrobium inconstans
3b. Sepals more than 4 cm long. == 4

4a. Sepals 4-4.5 cm long == Dendrobium inauditum
4b. Sepals 6.5 cm long == Dendrobium dilatatocolle

5a. Keels on the lip at least in part with (sub)crenulate or undulate crest == 6
5b. Keels on the lip with the crest straight, not undulating or (sub)crenulate == 15

6a. Keels on the lip at least in part with (sub)crenulate crest == 7
6a. Keels on the lip at least in part with undulating crest == 9

7a. Leaves narrowly linear, 20-25 by 0.3-0.4 cm. Flower c. 5 cm across. Keels in basal part papillose, to the apex subcrenulate, between the keels with a swollen median line, starting at c. 1/3 above the base, extending to c. 1/3 below the apex == Dendrobium gracilicolle
7b. Leaves ligulate or oblong oblong, 8-18 by 2.3-3 cm. Flower more than 7 cm across. Keels in basal part not papillose, crenulate from base to top, without swollen median line == 8

8a. Pedicel and ovary 4 cm long. Leaves oblong, 8-10 by 2.5-3 cm == Dendrobium mekynosepalum
8b. Pedicel and ovary 11 cm long. Leaves ligulate, 14-18 by 2.3-3 cm == Dendrobium xanthocaulon

9a. Keels extended from base of the hypochile to almost the tip of the epichile, the undulating part laxly undulate, in the top half of the endlobe closely parallel, straight == Dendrobium NOT guttulatum
9b. Keels extended from base of the hypochile to the top of the claw of the epichile, the undulating part of the keels densely undulate == 10

10a. Lateral lobes of the hypochile very pronounded and high to the apex and claw of the epichile distinctly tapering to the endlobe: hypochile and claw of epichile when flattened almost quadrangular, about as long as wide. Keels at the base of the hypochile straight and parallel, touching, then parting widely and undulating, enclosing a broadly elliptic papillose patch == Dendrobium isthmiferum
10b. Lateral lobes of the lip somewhat pronounded or not, and claw of the epichile not or hardly tapering to the endlobe: hypochile and claw of epichile when flattened not almost quadrangular, 1.5-2x as long as wide. Keels at the base of the hypochile straight and parallel but,not touching, then parting widely and undulating, enclosing a rectangular patch which is not papillose == 11

11a Sepals less than 2.7 cm long; lip c. 1.1 cm long == Dendrobium tipula
11b. Sepals more than 5 cm long; lip 1.3-1.4 cm long == 12

12a. Leaves 11-13 cm long. Hypochile when flattened semi-elliptic, without claw. Claw of epichile with hardly undulating margins and surface == Dendrobium longicolle
12b. Leaves 13–23.5 cm long. Hypochile when flattened spatulate, with a pronounced narrow claw. Claw of epichile with much undulating margins and surface == Dendrobium moiorum

13a. Lateral lobes of the lip very pronounded and high: hypochile and claw of epichile when flattened almost quadrangular in outline, about as long as wide. Keels 2, at the base of the hypochile straight and parallel, apart, then parting widely and enclosing a broadly rectangular pubescent patch == Dendrobium sitanalae
13b. Lateral lobes of the lip low and indistinct or very pronounded falcate: hypochile and claw of epichile when flattened not quadrangular in outline. Keels 3, 2 from the base of the hypochile straight and parallel, apart, then parting gradually and enclosing a narrow, elliptic glabrous patch with a median keel in between == 14

14a. Leaves ligulate-lanceolate, 10-12.5 by 2-2.5 cm == Dendrobium sitanalae
14b. Leaves linear, 8-10 by 0.43-0.5 cm == Dendrobium janowskyi

15a. Lateral lobes of the hypochile very pronounced, in front projecting, falcate. Keels on the hypochile largely touching, parallel, in front gradually slightly diverging, beyond halfway endlobe of epichile converging. Endlobe of epichile very large, when flattened semi-circular or reniform with broadly obtuse apex == Dendrobium iboense
15b. Lateral lobes of the hypochile not pronounced, in front receding. Keels on the hypochile apart, gradually slightly diverging, beyond halfway endlobe of epichile converging. Endlobe of epichile when flattened subcircular with apiculate tip == Dendrobium ischnopetalum



Genus Dendrobium section Diplocaulobium subsection Mekynosepalum contains the following 15 species, which all occur in New Guinea:

Dendrobium carinulatidiscum
Dendrobium dilatatocolle
Dendrobium gracilicolle
Dendrobium iboense
Dendrobium inauditum
Dendrobium inconstans
Dendrobium ischnopetalum
Dendrobium isthmiferum
Dendrobium janowskyi
Dendrobium longicolle
Dendrobium mekynosepalum
Dendrobium moiorum
Dendrobium pleurothalloides
Dendrobium sitanalae
Dendrobium tipula
Dendrobium tortitepalum
Dendrobium vanilliodorum
Dendrobium wantipiense
Dendrobium xanthocaulon