Taxonomy and morphology of Thalictrum (Ranunculaceae) in New Guinea

The genus Thalictrum L. in New Guinea is revised based on morphological evidence. Full descriptions of the genus and the four taxa recognised are given. Two species are recognised: Thalictrum papuanum, widespread across New Guinea, and a new species described here; T. umbraticola, endemic to west New Guinea. Two new varieties are described: Thalictrum papuanum var. acutisegmentum and T. papuanum var. laticarpellum. One new synonym of Thalictrum papuanum var. papuanum is established: T. papuanum var. oranjense. Keys to the taxa and distribution maps, as well as preliminary conservation assessments, are provided.


Introduction
Ranunculaceae are a cosmopolitan family that includes many well-known temperate wildflowers and ornamental plants, including buttercups, hellebores and anemones, as well as several pharmaceutically important taxa. According to the Plants of the World Online (POWO 2019), there are 52 accepted genera and 3766 accepted species of Ranunculaceae. The family is distributed almost worldwide but is most diverse in temperate and colder regions; it is relatively rare in the tropics (Culham 2007). Ranunculaceae are thought to have originated in montane temperate areas of the northern hemisphere (Ziman & Keener 1989). The family shows a wide variation in morphological characters, especially in floral organisation and fruit types (Tamura 1995). In New Guinea, three genera are present: Clematis L., Ranunculus L. and T h a l i c t r u m L . (C á m a r a -L e r e t et al . 2 0 2 0 ) . Ranunculaceae of Malesia have been revised by Eichler (1958), and the alpine species have been treated by van Royen (1982) and more recently in Utteridge (2006). Most species occur at high elevations; for example, in a checklist of Mt Trikora, Mangen (1993) documented 16 species of Ranunculaceae, with 14 taxa above and only two taxa below 3000 m.
As part of ongoing research into the plant diversity and conservation of New Guinea at the Royal Botanic Gardens, Kew, the genera of Ranunculaceae on the island are being revised as the first stage towards a Flora Malesiana account. As part of this work, a revision of Thalictrum is presented here. Upon investigation it was found that the existing species, Thalictrum papuanum, did not fit all the material examined during this work. To account for all the variation, a new species was described as well as two further varieties.
The genus Thalictrum was first described by Linnaeus (1753: 545) and is considered one of the most diverse genera in the family in terms of the number of species and their morphological variation (Tamura 1995). It has T(= Thalictrum)-type chromosomes with the basic chromosome number x = 7 (Tamura 1993) and is included in the subfamily Thalictroideae (Wang et al. 2009). Thalictrum has great medicinal value as several species contain high levels of an anti-tumour drug, Thaliblastin (Thalicarpine) (Chen et al. 1993;Pajeva et al. 2004). All seeds of Thalictrum species investigated so far contain four unusual and diagnostically important fatty acids; two of these are the same as in Aquilegia L., whereas two have not been found in any other genus in Ranunculaceae (Aitzetmüller 1994). Comprising over 200 species (POWO 2019), Thalictrum is distributed in Eurasia, Americas, Africa and New Guinea (Mabberley 2008;Stevens 2001 onwards). In New Guinea it is represented by four endemic taxa (two species and two varieties).

Materials and Methods
Herbarium material and especially types deposited at B, BM, BO, CANB, E (online), GH, K, L, LAE, LUX (online), MU, P (online) and SING (online) were examined. Herbarium acronyms follow Index Herbariorum (Thiers, continuously updated). All cited specimens have been seen by the first author. Material was examined under a Leica M165 C binocular microscope at maximum magnification.
Nomenclatural practice follows Turland et al. (2018). Characters listed in the protologues and descriptions were compared to those present in herbarium material. Morphological terms follow Beentje (2016). Localities were manually georeferenced using locality information from herbarium specimens, paper maps and electronic gazetteers. Maps were made using Simple Mappr (Shorthouse 2010) with additional layers showing countries and relief. Assessment of conservation status was implemented using GeoCAT (Bachman et al. 2011) and follows the IUCN (2012) criteria.
DISTRIBUTION. About 190 species, worldwide, mainly in temperate regions; two species in New Guinea.

Key to the species of Thalictrum in New Guinea
Herbs 4 -30 cm tall. Petiole of cauline leaves 1 -10 mm, petiolule of cauline leaves 1 -5 mm. For type and synonyms see varieties.

RECOGNITION.
Thalictrum umbraticola is unique in the following combination of characters: style circinnately coiled inwards at apex, 6 -9 achenes, 1 -2-ribbed on each side, 3.5 -5.5 × 0.5 mm, basal leaves few, blades up to 9 cm long with leaflets up to 1.8 cm long and it grows at relatively low elevations (1200 -1300 m), under arching limestone rock, in very damp and rather dark habitat. DISTRIBUTION HABITAT. Under arching limestone rock, very damp, rather dark, lower montane forest; elevation: 1200 -1300 m. CONSERVATION STATUS. Due to sparsity of herbarium material and in the absence of information on threats, a conservation category of Data Deficient (DD) is proposed for this species; having only two collections does not allow us to calculate EOO or AOO. Further surveys in the area are recommended. PHENOLOGY. Flowering and fruiting from Jan. to May. ETYMOLOGY. From the Latin umbra, shade, and -cola, dweller, referring to the shady habitat of this species. NOTES. Thalictrum umbraticola is morphologically close to T. javanicum Blume and T. uncatum Maxim. (as delimited by Zheng et al. 2018) in height, glabrous habit and styles hooked at apex. It differs conspicuously from T. javanicum in the basal leaves (T. umbraticola biternate vs T. javanicum 3 -4 ternate), stipitate achenes (stipe 0.5 -1 mm vs achenes sessile) and style length (1 -2 mm vs 0.6 -1 mm); and from T. uncatum in leaf blade size (3 -7 × 3 -9 cm vs 9.5 -13 × 15 cm) and style length (1 -2 mm vs 2.2 -3 mm). It differs from both in the smaller sepals (2 × 1 mm), fewer stamens (15), shorter filaments ((1.5 -) 2 -2.5), shorter anthers (0.5 mm) and fewer carpels (6 -9). M.L. (SING). The comments and suggestions of two anonymous reviewers were extremely useful and we thank them for helping to improve the manuscript; we also thank Carmen Puglisi for useful discussions and constructive comments.
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