Larsenianthus W. J. Kress & Mood, 2010

Kress, W. John, D. Mood, John, Sabu, Mamiyil, Prince, Linda M., Dey, Santanu & Sanoj, E., 2010, Larsenianthus, a new Asian genus of Gingers (Zingiberaceae) with four species, PhytoKeys 1, pp. 15-32 : 19-20

Larsenianthus W. J. Kress & Mood gen. nov. Figs. 2-4 Plate 1A-D

Latin

Zingiberacearum tribus Zingiberearum genus novum Hedychio J. Koenig affine, a quo staminodiis lateralibus parvis auriculatis, labello angusto elongato marginibus incrassatis carinaque centrali et filamento valde arcuato differt.

Type.

Larsenianthus careyanus (Benth.) W. J. Kress & Mood, comb. nov., Hitchenia careyana Benth., Gen. Pl. 3: 643. 1883.

Description.

Evergreen, rhizomatous, terrestrial herbs, clumping with 10-20 shoots per plant, 1-2.5 m tall, plane of distichy of leaves parallel to rhizome, 2-12 leaves per shoot, alternate, sessile to petiolate. Inflorescence terminal on leafy shoot or basal on leafless shoot, pedunculate; bracts basally attached, reflexed or adpressed, spirally arranged and imbricate, 35-80 per inflorescence, not pouched, adventitious plantlets sometimes produced in sterile bracts at base of inflorescence; flowers mature from base to apex of inflorescence. Bracteoles variable in size, the inner one largest, not tubular. Flowers conspicuous, in cincinni of 2-6 flowers or rarely reduced to one flower; calyx tubular, tri-dentate, shorter than the corolla; floral tube long and curved, exserted well beyond the bract, corolla lobes subequal with dorsal lobe slightly larger than laterals, apex opening oblong, bordered on the two lateral sides with a thickened and rounded margin formed by the base of the lateral staminodes and the labellum; lateral staminodes small, bowl-shaped, reflexed; labellum narrow at the base, widening towards the apex, elongate, oblanceolate or spatulate, basal margins thickened, raised with center channeled or ‘v’ in cross-section, apex dentate or entire; fertile stamen long and arched over the labellum, anther oblong, without a crest, thecae dehiscent for full length; epigynous glands linear; style with stigma protruding beyond anther thecae; ovary trilocular, fruit an oblong capsule, two-layered with the outer splitting into three coiled sections, the inner forming an arillate membrane covering the 1-10 seeds.

Discussion.

Larsenianthus is a distinctive genus in the tribe Zingibereae. Some similarities exist with the genera Hedychium , Globba and Pommereschea in the vegetative parts, the bract orientation, and the long filament. The uniqueness of the genus and its close relationship to Hedychium is confirmed by phylogenetic analyses of DNA sequence data ( Fig. 1 ). However, the combination of unique features including the narrow, elongate labellum with slightly thicken edges and a deeply channeled center combined with the small, cup-shaped lateral staminodes and strongly arched filament clearly distinguish this genus from others in the tribe. Two additional traits that ch aracterize at least two of the four species in the genus ( Larsenianthus assamensis and Larsenianthus careyanus ) are the unusual white capsular fruit with a gelatinous fused arillate structure that encases the seeds and the multiple adventitious plantlets that form in the axils of the sterile bracts at the base of the inflorescence.

Etymology.

This new genus honors Dr. Kai Larsen, Professor of Botany Emeritus, Aarhus University, Denmark, for his many years of dedicated efforts in the education of botanists worldwide and for his profound achievements in the taxonomy of the family Zingiberaceae , especially in the flora of Thailand.

Key to species of Larsenianthus

.

1b.	Inflorescence terminal on a leafy shoot	2
2a.	Inflorescence bracts green and white, 4-6 flowers per bract	Larsenianthus careyanus
2b.	Inflorescence bracts red, 1-3 flowers per bract	3
3a.	Margins of inflorescence bracts corrugate and denticulate, 1 flower per bract	Larsenianthus assamensis
3b.	Margins of inflorescence bracts entire and smooth, 2-3 flowers per bract	Larsenianthus arunachalensis

Figures

Plate 1. Inflorescences with flowers of A Larsenianthus wardianus W. J. Kress, Thet Htun & Bordelon B Larsenianthus careyanus (Benth.) W. J. Kress & Mood C Larsenianthus assamensis S. Dey, Mood, & S. Choudhury D Larsenianthus arunachalensis M. Sabu, Sanoj & T. Rajesh Kumar. All photos by the authors.

Figure 1. Molecular phylogeny of the Zingiberaceae indicating the placement of Larsenianthus within the Zingiberoideae in the combined ITS / trnK analysis. Tree length (excluding uninformative characters) = 1,590 steps, Consistency Index = 0.5314, Retention Index = 0.6809, Rescaled Consistency Index = 0.3619. Bootstrap numbers are provided above the branch, Posterior Probabilities below.

Figure 4. Larsenianthus arunachalensis M. Sabu, Sanoj & T. Rajesh Kumar. A inflorescence B apical part of leaf sheath with ligule and petiole C inflorescence bract D bracteole E calyx F flower, lateral view G floral tube H labellum I lateral staminodes J anther, front, back and lateral views K unicellular branched hairs inside corolla tube L stigma and upper portion of style M base of flower, cut-way view to show style and epigynous nectaries N ovary, transverse section. Line drawing by E. Sanoj from plants in cultivation; voucher Sanoj & Rajesh Kumar 105640.