Decaisnina Tieghem. Bull. Soc. Bot France 42 (1895) 434, 435. - Type: D. glauca Tieghem [= D. triflora (Spanoghe) Tieghem].

For descriptions and synonymy see Barlow, Austral. J. Bot. 22 (1974) 535; Flora of Australia 22 (1984) 74. Danser (1931) included Decaisnina in Amylotheca, which was more broadly circumscribed than in this treatment.

A genus of 25 species distributed from Java, Celebes and the Philippines eastwards to New Guinea, Australia and across the South Pacific to Tahiti and the Marquesas. The major centres of species richness and diversity are the Philippines and New Guinea (see below). Range extension to oceanic Pacific islands involves only one species, D. forsteriana, which has achieved the widest distribution by distance dispersal of any loranth species.

The species are found in a range of habitats from rain forests to open tropical woodlands and monsoon scrubs, and from lowland to montane forests. Attachment to the host is exclusively through secondary haustoria on extensive epicortical runners. Leaf architecture is not very variable, ranging from a common simple bifacial pattern to thick or thin isofacial forms, always decussate and with pennate venation. Most variation is in inflorescence and flower structure, and is apparently related to pollination. Host specificity is generally low, but may be moderately high in open seasonally arid woodlands.

Diagnostic features
The infrafamilial classification of Decaisnina and the generic group to which it belongs is outlined above. For identification at the generic level the readily observable morphological characters are derived from inflorescence and flower structure.

The basic inflorescence unit (uniflorescence) in Decaisnina is a simple dichasium (triad) with a simple bract subtending each flower. The triads are aggregated into conflorescences, and the plesiomorphic state for the genus is an axillary raceme of uniformly spaced opposite pairs of triads. In many of the species the inflorescence is presented horizontally and the triads are secund, all turning upwards on their peduncles so that the inflorescence has a brush-like appearance. Simpler inflorescences are probably derived by reduction, but always comprise one or more pairs of triads in a racemose arrangement.

The flowers of Decaisnina are hermaphrodite, 6- or rarely 5-merous, regular and basically choripetalous, although in the majority of species the petals remain weakly coherent in the lower part after anthesis. In some species the short corolla tube so formed is dilated to form a distinct nectar chamber. The epipetalous stamens have basifixed immobile introrse anthers with simple filaments which in some cases are very short so that the anther is subsessile. The style is usually articulate above the base, leaving a distinct nipple on the fruit.
Vegetative features are relatively homogeneous. Sessile or almost sessile cordate leaves are constant or occasional in several species of Decaisnina, and occur in species which are otherwise distinct in an array of other vegetative and reproductive characters. The condition is probably of multiple origin in the genus, perhaps as one of several modifications which appear to protect the developing inflorescence.

Generic relationships
Decaisnina is the largest genus in the group, and probably the least specialized. The related genera are all small, each characterized by a single distinctive feature, and apparently derived. In some cases the derived genera are characterized by capitate inflorescences subtended by well-developed involucres, apparently evolved convergently as adaptations for protection and/or presentation of the flowers. The homologies of these inflorescence structures are discussed under the individual genera, but it is noteworthy that most of the relevant basic structures are present in at least some of the species of Decaisnina.
The present study has revealed especially close links between Decaisnina and the unusual genus Cyne. In the latter genus the inflorescence is a sessile or subsessile capitulum or very condensed raceme formed from sessile or subsessile decussate triads, and therefore derivable from Decaisnina by reduction. The distinctive feature in Cyne is the development of the inflorescence in a hollow of the stem, below the periderm, which forms a blister-like operculum which lifts off, or through which the inflorescence emerges, as the flowers enlarge. The inflorescences in some species of Cyne show a clear transition in degree of reduction from those of Decaisnina. See notes under Cyne.

Biogeographic history
See notes above on the biogeography of the decaisninoids. Decaisnina is a distinctive genus in having a balanced distribution across Charles's Line, with centres of species richness on both the Sunda and Australo/Papuasian plates. It was presumably well represented in the intrusive Malesian stocks which penetrated New Guinea and northern Australia, and underwent significant differentiation and speciation in the process. Being basically a lowland genus, its distribution and differentiation have probably been influenced by the cyclic changes in climate and sea level which have succeeded the initial exchange. This is possibly why Decaisnina is taxonomically one of the most difficult genera of the entire region.

la. Inflorescence subtended by an involucre of decussate scales at the base of the axis 2
1b. Inflorescence not subtended by an involucre of decussate scales at the base of the axis 6
2a. Inflorescence axis oriented vertically with the flowers not strongly secund; lateral flowers of the triads on distinct pedicels at least as long as the ovary 3
2b. Inflorescence axis oriented horizontally with the flowers strongly secund, giving the inflorescence a brush-like appearance; lateral flowers of the triads on obscure pedicels much shorter than the ovary 5
3a. Stems and inflorescence parts very thick; internodes short and often crowded so that the leaves appear verticillate; corolla more than 30 mm long (Philippines) 24. D. viridis
3b. Stems and inflorescence parts slender to moderately robust; internodes normally developed with evenly spaced decussate leaf pairs; corolla less than 30 mm long 4
4a. Inflorescence axis less than 15 mm long; corolla 5-merous, hardly inflated at the base (Philippines) 17. D. ovatifolia
4b. Inflorescence axis more than 30 mm long; corolla 6-merous, distinctly inflated at the base (Philippines) 1. D. aherniana
5a. Leaf lamina up to 8 cm long; triads crowded at the end of the inflorescence axis (Philippines) 19. D. revoluta
5b. Leaf lamina more than 10 cm long; triads distributed uniformly along the inflorescence axis (Philippines) 9. D. crassilimba
6a. Leaves sessile, truncate to amplexicaul at the base 7
6b. Leaves petiolate, or if sessile attenuate at the base 10
7a. Anther almost sessile (with free filament less than 1 mm long) 8
7b. Anther with free filament more than 1.5 mm long 9
8a. Corolla less than 20 mm long; young internodes angular (Philippines, Moluccas) 10. D. cumingii
8b. Corolla more than 20 mm long; young internodes soon terete (Philippines) 16. D. miniata
9a. Leaf lamina dull on both sides (Australia) 20. D. signata
9b. Leaf lamina bifacial, glossy on the upper surface (Philippines, New Guinea) 2. D. amplexicaulis
10a. Leaves distinctly bifacial with upper surface glossy or darker than the dull lower surface 11
10b. Leaves dull and more or less the same colour on both sides 17
11 a. Corolla less than 10 mm long; anthers nearly sessile (New Guinea) 15. D. micranthes
11b. Corolla 10-22 mm long; anthers sessile or nearly so 12
11c. Corolla more than 22 mm long; anthers on distinct free filaments more than 2 mm long 13
12a. Young internodes 4-angular; leaf lamina strongly bifacial, recurved at the margin; inflorescence and flowers shortly and densely tomentose (Philippines) 7. D. confertiflora
12b. Young internodes dilated and 2-angled in the upper part; leaf lamina weakly bifacial, not recurved at the margin; inflorescence and flowers glabrous or sparsely hairy (Philippines, Moluccas) 10. D. cumingii
13a. Stems and inflorescence parts very thick; internodes short and often crowded so that the leaves appear verticillate; corolla inflated to 5 mm wide in the lower part (Philippines) 24. D. viridis
13b. Stems and inflorescence parts slender to robust; internodes normally developed with evenly spaced decussate leaf pairs; corolla not or slightly inflated at the base 14
14a. Triads in 1-3 pairs crowded near the apex of the inflorescence axis; leaves narrowly elliptic (New Guinea, Australia) 8. D. congesta
14b. Triads in several pairs distributed uniformly along the inflorescence axis; leaves ovate 15
15a. Petals eventually separating to the base; anthers transversely septate prior to anthesis (Solomon Is. to Tahiti and Marquesas) 12. D. forsteriana
15b. Petals remaining coherent in the lower part; anthers not transversely septate 16
16a. Plant robust, usually with a short brown tomentum on the young parts and inflorescences; leaves with a distinct petiole mostly more than 10 rom long and lamina strongly bifacial; corolla mostly more than 30 mm long (New Guinea, Solomon Is.) 13. D. hollrungii
16b. Plant relatively slender, glabrous or rarely with the inflorescence sparsely pubescent; leaves with a petiole mostly less than 10 mm long and lamina weakly bifacial; corolla less than 30 rom long (Philippines, Celebes, Lesser Sunda Is., New Guinea) 22. D. sumbawensis
17 a. Corolla inflated and globular atthe base 18
17b. Corolla not inflated at the base, or if so then not sharply contracted to form a globular dilation 20
18a. Corolla less than 20 mm long (Philippines, Moluccas) 10. D. cumingii
18b. Corolla more than 20 mm long 19
19a. Young internodes strongly angular distally 25. D. zollingeri
19b. Young internodes not strongly angular distally 21. D. stenopetala
20a. Leaves linear to lanceolate 21
20b. Leaves broadly lanceolate to orbicular 23
21a. Internodes strongly flattened (Australia) 4. D. biangulata
21b. Internodes terete except when very young 22
22a. Leaves attenuate at the base to an obscure petiole, often falcate (Australia) 5. D. brittenii
22b. Leaves truncate or cordate at the base, almost sessile, usually not falcate (Australia) 20. D. signata
23a. Corolla less than 10 mm long; anthers nearly sessile (New Guinea) 15. D. micranthes
23b. Corolla 10-20 rom long; anthers sessile or nearly so (Philippines, Moluccas) 10. D. cumingii
23c. Corolla more than 20 mm long; anthers on distinct free filaments more than 2 mm long 24
24a. Triads crowded near the apex of the inflorescence axis 25
24b. Triads distributed uniformly along the inflorescence axis 26
25a. Leaf lamina acuminate, acute at the apex; corolla 35-50 mm long (Celebes) 6. D. celebica
25b. Leaf lamina obtuse to rounded at the apex, often with a small blunt mucro; corolla 23-30 mm long (New Guinea, Australia) 8. D. congesta
26a. Corolla pale green or yellow in the lower part; petals separating to the base at anthesis (New Guinea) 11. D. djamuensis
26b. Corolla red in the lower part; petals cohering in the lower 1-15 mm after anthesis 27
27a. Triads with all flowers sessile 28
27b. Triads with the central flower sessile and the lateral flowers pedicellate. 30
28a. Petals usually coherent for more than 2 mm; anther mostly slightly shorter than the free part of the filament (Lesser Sunda Is, Moluccas, New Guinea, Australia) 23. D. triflora
28b. Petals coherent in the lower 0-2 mm; anther mostly longer than the free part of the filament 29
29a. Lamina truncate or cordate at the base, sessile or nearly so (Australia) 20. D. signata
29b. Lamina attenuate at the base into an obscure winged petiole (Australia) 3. D. angustata
30a. Leaf lamina broadly lanceolate to elliptic, attenuate at the base to an obscure petiole 3-5 mm long; corolla 23-30 mm long (New Guinea) 18. D. pedicellata
30b. Leaf lamina elliptic to almost orbicular, shortly cuneate at the base with a distinct petiole 25-40 mm long; corolla 30-50 mm long (New Guinea) 14. D. longipes

last updated 25 June 2003