Research Article |
Corresponding author: Hirokazu Tsukaya ( tsukaya@bs.s.u-tokyo.ac.jp ) Academic editor: Murielle Simo-Droissart
© 2017 Izai Alberto Bruno Sabino Kikuchi, Hirokazu Tsukaya.
This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY 4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Citation:
Kikuchi IABS, Tsukaya H (2017) Epitypification with an emended description of Tropidia connata (Orchidaceae, Epidendroideae, Tropidieae). PhytoKeys 80: 77-85. https://doi.org/10.3897/phytokeys.80.12304
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We found several specimens of Tropidia connata, a mycoheterotrophic orchid from Borneo, with features which have never been described in any of the existing literature, namely subterranean tubers. We mainly focus on the importance of the subterranean structures in comparison with the mycoheterotrophic genus Kalimantanorchis from the tribe Tropidieae. This finding of the tuberous structure gives a new insight into the classification of mycoheterotrohic species of Tropidieae and might affect the generic placement of Kalimantanorchis. We made a detailed study on the newly discovered specimens as well as the type, and found more diagnostic characters of T. connata than the previous description. Considering that the type specimen lacks the whole tuberous character, we consequently designate an epitype with a drawing and emend the description.
Borneo, emendation, epitypification, Kalimantanorchis , mycoheterotroph, Orchidaceae, Tropidia , Tropidieae
The genus Tropidia Lindl. (Orchidaceae, Epidendroideae, Tropidieae) currently contains about 30 species mainly distributed from Far East Asia, India, Sri Lanka, Indochina, Malaysia, Indonesia, the Philippines and New Guinea to northern Australia, spreading across the South Pacific Islands. There is one exception to this distribution: Tropidia polystachya (Sw.) Ames is native to Florida, the West Indies, Central America and northern South America including the Galapagos Islands (
Due to the rare occurrence of the mycoheterotrophic species in general and to the difficulty in extracting a complete root system, the subterranean parts of most mycoheterotrophic plants are less known than their aerial parts (
We collected three specimens from three localities of Indonesia under permission of Secretariat of Permission for Foreign Research, The Ministry of Research and Technology, Republic of Indonesia (RISTEK). The specimens (two of which are with tubers) were examined in this study. We also examined the type specimen, A.Lamb, A.Surat & H.Lim 1512 (K000942868). The newly collected specimens were dried or kept in 50% (v/v) ethanol and deposited in both BO and TI (herbarium codes are according to the Index Herbariorum http://sweetgum.nybg.org/science/ih/). The type specimen is deposited in K. Morphological observation was carried out using a stereomicroscope (MZ16a; Leica Microsystems). All measurements were taken from dried and spirit herbarium collections and field notes. The measurements are presented as length × width, followed by units of measurements (mm or cm). The terminology used here is according to
In the original description, the diagnostic characters of Tropidia connata are the fractiflex rachis, connate lateral sepals forming a synsepalum, and shortly spurred lip (
The most distinct feature that had not been described in the previous description is the subterranean tuberous structure (Figures
Drawing of Tropidia connata J.J.Wood & A.L.Lamb. A Gross morphology B Lateral view of unopened flower C Lateral view of the column with lip D Dorsal view of the column E Lip F Anther cap G Pollinia H Lateral view of the column I Dorsal sepal J, K Lateral petal of abaxial (J) and adaxial (K) side. L Lateral sepal M Tuber with basal part of inflorescence with short filamentous roots. Scales 3 cm (A), 3 mm (B, C, I–K), 1 mm (D–H), 5 mm (M). Drawing by Ms. Mutsuko Nakajima based on the specimen HT245.
The second distinct feature observed for the first time here is the two fiber-like protrusions attached to the adaxial side of the stigma (Figure
Another distinct feature recognized is the difference between the scale-like leaves and the flower bracts. While 5-10 scale-like leaves are seen on the stem and are ovate, acute, adpressed to the stem (N = 7) (Figure
We did not find any specimens with fully matured fruits, so we could not make an observation of the fruits or the seeds, which are also undescribed in the original description.
Tropidia connata J.J.Wood & A.L.Lamb. A Gross morphology of two individuals (specimen number 1040, collected in January 5, 2011). Scale in cm B Close-up of the inflorescence C, D Part of inflorescent stem with bracts showing before (C) and after (D) the detachment of the apical part at the abscission zonev E Subterrestrial part of the flowering individual. Divisions of scale in mm.
The tribe Tropidieae contains the genera Tropidia, Corymborkis Thouars, and the monotypic and mycoheterotrophic Kalimantanorchis Tsukaya, M.Nakaj. & H.Okada. Corymborkis does not contain any mycoheterotrophic species.
The presence of underground tubers has never been described in the genus Tropidia, although it was described for Kalimantanorchis nagamasui Tsukaya, M.Nakaj. & H.Okada (
This discovery of the tuberous structure of T. connata clearly indicates that this is a shared feature of two of the mycoheterotrophic species in the tribe Tropidieae. However, the presence of a tuber has also never been reported for the other mycoheterotrophic species of Tropidieae, T. saprophytica. We consider that it is of great importance to discover new samples of T. saprophytica with well-preserved subterranean parts as well.
The main morphological feature of Kalimantanorchis, which made it distinct from other Tropidia mycoheterotrophic species at the time it was discovered, is the presence of the tubers. This result therefore raises the possibility that the genus Kalimantanorchis is not distinct from the genus Tropidia or that the tuber structure separately evolved in the tribe Tropidieae more than twice. The previous phylogenetic analyses of Kalimantanorchis (
In addition to the tuberous structure, we found an abscission layer on bracts and two fibrous protrusions attached to the adaxial side of the stigma, both of which have never been described for other mycoheterotrophic Tropidieae species. The presence of such protrusions implies that there may have been some change in the pollination systems for T. connata due to the fully mycoheterotrophic habitat. Further research is needed to examine the function of these fibers in the pollination system to understand the possible pollination change in this species.
The subterranean part of the type specimen was badly preserved as it lacks whole tuberous parts. Judging from the importance of this new finding of the tuberous structure, which provides possible changes in the classification of the tribe Tropidieae, we therefore consider it is necessary to choose one of the newly collected specimens (HT245) as an epitype. We designate the epitype, provide a drawing of the epitype, and emend the description of Tropidia connata at the end of this section as a taxonomic treatment.
Following this research, we conclude that the tribe Tropidieae is not thoroughly understood and little work has been done through either morphological or molecular methods. In particular, no comprehensive research of the whole genus Tropidia has been done, though this genus has a morphologically unique subterranean tuberous structure, and it seems that there still remain a lot of complications in this genus. It is also important to mention that several species have been discovered recently (
MALAYSIA. Borneo: Sabah, Sipitang District, Gunung Lumaku, 27 June 1992, A.Lamb, A.Surat, & H.Lim 1512 (holotype: K!, K000942868).
INDONESIA. West Kalimantan: Kabupaten Kapuas Hulu, Betung Kerihun National Park, en route from stream to ridge, a branch of Sungai (River) Sibau, 01°13.32'N; 113°06.2433'E, 240 m alt., 31 December 2011, H. Tsukaya, H. Okadada and A. Soejima HT245 (BO, TI), here designated.
Erect, mycoheterotrophic herb. Tubers 2–7×0.5–1 cm, dark brown, pubescent. Roots 2–5 mm long, short, occurring at the basal 1–3 nodes of stem. Stem 10–22 cm high, ivory white to creamy colored, wiry, simple or branched, perennial, 1 mm thick, internodes 0.8–2.5 cm long, sparsely ramentaceous, bearing 5–10 ovate, acute, sheath-like leaves apressed to the stem, 3–5 mm long. Inflorescence 5–15 flowered, 1–2 flowers open at a time; rachis 2–9 cm long, creamy white, internodes 4–10 mm, slightly zigzag, sparsely ramentaceous; floral bracts 3–5 mm long, off white tipped brown, triangular, acute to acuminate, with a abscission zone at 1–2 mm from the apex, apex detached at the abscission zone after maturation, base of the bracts forming a sheath enclosing the stem. Flowers 1 cm across, non-resupinate, partially open, white, apex of the lip pale orange to yellow. Pedicel with ovary 3–7 mm long, white, sparsely ramentaceous. Dorsal sepal 5–5.9×1.5–1.8 mm, narrowly elliptic, acute, sparsely ramentaceous on the abaxial sides. Lateral sepals connate into a 4–7.4×2.5–2.7 mm ovate-elliptic, cymbiform synsepalum, apex minutely bifid. Petals 4.8–6×1.5 mm narrowly elliptic, acute and asymmetric with two keels at the adaxial surface. Lip 5–7.6×2–2.2 mm with 3 nerves, elliptic, acute, concave, margin minutely erose, curving back to a horizontal position, spur saccate, obtuse, bifid, enclosed by synsepalum, 1.1–4×1 mm. Column 3–3.9×1.6–1.9 mm, ovate-trullate rostellum margin minutely erose 1.4–1.5 mm long, anther cap rostrate 2.5 mm long, stigma with calli-like protrusions and two fiber-like protrusions on the adaxial side of the column, the fibers 1.1–1.4 mm long. Pollinia 2, granular. Vicidium ellipsoid.
INDONESIA. West Kalimantan: Kabupaten Kapuas Hulu, Betung Kurihun National Park, Sungai (River) Menyakan, upstream of Sg. Sibau, 01°13.825'N; 113°03.963'E, 331m alt. to 01°13.82167'N; 113°03.9367'E, 331 m alt., 5 January 2011, H. Tsukaya, H. Okada and H. Nagamasu #1040 (BO, TI); Kabupaten Kapuas Hulu, Betung Kerihun National Park, on a ridge the junction of Sungai (River) Sibau and Sungai Minyakan, from 01°12.5567'N; 113°04.35'E, 298 m alt. to 01°12.325'N; 113°04.433'E, 341 m alt., 1 January 2012, H. Tsukaya, H. Okadada and A. Soejima HT250 (BO, TI).
The authors wish to thank the Secretariat of Permission for Foreign Research, The Ministry of Research and Technology, Republic of Indonesia (RISTEK) for kindly giving us the permission to conduct the expeditions in West Kalimantan. We would like to thank the curators and collaborators at the Indonesian Institute of Science (LIPI) for kindly supporting the study in the Betung Kerihun National Park, West Kalimantan. We also thank Dr Hiroshi Okada of Osaka City Univeristy, Dr Hidetoshi Nagamasu of Kyoto University, Dr Akiko Soejima of Kumamoto University, Dr Dedy Daernadi of LIPI, Mr Ujang Hapid of Herbarium Bogoriense (BO), Mr Mustarr Udin, Suherman, Jon, Anong, Mazid, and Eddy for helping to conduct the botanical surveys during the expedition. Mr Arief Hidayat of Herbarium Bogoriense kindly guided us through the complex procedure of obtaining research permission. We are grateful to Mutsuko Nakajima for making the beautiful and very helpful illustration of Tropidia connata. Prof. Jin Murata, Dr Tetsuo Ohi-toma at the Botanical Gardens of the Univ. Tokyo, Dr Jorinde Nuytinck at Naturalis Biodiversity Center and Ben Gable at Leiden University are also appreciated for reviewing the first draft of this manuscript. The last author was financially supported by Grants-in-Aid from the Asahi Glass Foundation.