Taxonomic revision of Disporum Salisb. (Colchicaceae, Uvularioideae) of Taiwan

Abstract A taxonomic revision of Disporum of Taiwan is presented with two species and one variety being recognised. The diagnostic characters of Disporum include the colour of tepals, stolon morphology, the trichomes of filaments and style and leaf morphology. These characters, along with karyotype and pollen morphology, are discussed and evaluated amongst different taxa. As a result, D.kawakamii and D.shimadae are treated as independent species, rather than varieties of D.cantoniense and D.sessile, respectively. Disporumnantouense is treated as a synonym of D.sessilevar.intermediumstat. nov. Detailed descriptions, type information, diagnostic key, line drawings, photos and distribution maps are provided.


Introduction
Disporum Salisb. comprising of about twenty species, is distributed from the Himalayas through Vietnam, China, Japan, Korea and Russia. More than fourteen species have been found in China , four species are recorded in Japan (Tamura 2016) and four species are recorded in Taiwan (Ying 2000). Some new species have recently been described (Hu et al. 2016;Hareesh et al. 2018). This genus is characterised by having fleshy roots, erect stems with scale leaves at the lower part, pendulant flowers and berries, diagnostic characters of intrageneric taxa dependent on whether stolons are present, tepals spreading or not, colour and shape of tepals, length and trichome type of filaments and styles and colour of fruits (Hara 1988;Chen et al. 2000).
Taiwanese species have been studied by several authors from a morphological and karyological standpoint (Matsumura and Hayata 1906;Kawakami 1910;Hayata 1911;Chao et al. 1963;Liu and Ying 1978;Hara 1988;Ying 1989;Ying 1990ab;Wang 1997;Ying 2000), but each author had his/her own way of treating different ranks. Chao et al. (1963) recognised two species, D. kawakamii and D. shimadae, Liu andYing (1978) three species, D. kawakamii, D. pullum Salisb. &Hook. f., andD. shimadae andHara (1988) Hara. Ying (2000) treated the genus as consisting of four species D. kawakamii, D. nantouense Ying, D. shimadae and D. taiwanense S. S. Ying. Recently, in studying Liliaceae s. l. of Taiwan, we found that the diagnostic characters of Disporum were highly variable; moreover, the taxonomy of the species occurring in Taiwan has been confused by different authors. Therefore, we deemed that a revision of Disporum of Taiwan was necessary. In this study, we revise the genus by reviewing the literature and examining type specimens in herbaria, along with comparisons of the morphology, chromosome number and pollen morphology of specimens and establishing their distribution.

Materials and methods
The study materials were collected from the field and from herbarium specimens. Living plants were cultivated in the greenhouse of the Department of Forestry, NCHU. All voucher specimens were deposited in the herbarium of the Department Forestry, National Chung Hsing University (TCF). Specimens from the following herbaria specimens were examined: CHIA, HAST, KYO, PPI, TAI, TAIE, TAIF and TI (acronyms following Thiers, 2019, continuously updated).

Pollen morphology
Pollen was collected from fresh anthers of flowers in anthesis. Voucher specimens (Table 1) were deposited in TCF. The pollen samples were fixed in 70% ethanol (EtOH) and serially dehydrated with 80%, 90%, 95%, 99.5% EtOH and lastly with acetone. After drying with the Quorum E3100 critical-point dehydrator, the pollen specimens were observed and photographed with a scanning electron microscope (HITACHI S-3400N). Descriptions of pollen morphology used the terminology of Punt et al. (2007) and Hesse et al. (2009). Distribution and conservation rank rvaluation The distribution of each taxon was determined from the data on herbarium sheets and from our own field records. Only recognised specimens were marked on the map. The conservation rank evaluation followed the protocols of The Red List of Vascular Plants of Taiwan, 2017 (editorial committee of The Red List of Vascular Plants of Taiwan 2017).

Habit
The habit of Disporum in Taiwan includes two types, evergreen and deciduous. The evergreen type includes only D. kawakamii and the deciduous type includes two other taxa. The above-ground part of the deciduous types dies back in winter, leaving a dormant bud above the roots. The bud sprouts in the spring and grows up to form a new stem. The evergreen species produces similar buds at the same position, but the aboveground parts do not die back in winter and last into the next year.

Roots and stolons
The roots of Disporum are fleshy and glabrous without root hairs, which is a diagnostic character of the genus. Amongst the Taiwanese species, stolons are present in D. sessile var. intermedium and D. shimadae, but absent in D. kawakamii. The stolon is subterranean and creeping and the terminal bud becomes the new individual plant.

Leaves
The leaves of Disporum are simple, alternate, subsessile, glabrous and with an entire margin and stipules. The shape could be classified into two types, lanceolate to linearlanceolate and elliptic to oblong. The former includes D. sessile var. intermedium and D. shimadae and the latter D. kawakamii. Although the leaf shape of D. kawakamii is often elliptic to oblong, narrower leaves could be found on some individuals.

Inflorescence and flowers
The inflorescences of Disporum are pseudo-terminal and umbellate, with pendulous flowers. The flower is comprised of six tepals, six stamens and a pistil. The tepals are variable in shape and have a short gibbous spur and nectary. They are variable in colour, but in Taiwan are white, yellow or variable in colour. White tepals are found in D. sessile var. intermedium, yellow in D. kawakamii and D. shimadae. The apices of the tepals of D. sessile var. intermedium often have purplish or reddish spots, respectively. Some populations of D. kawakamii have deeper colouration and these had been described as a new species, D. taiwanense, based on this character; but the colour can vary with the habitat: the more exposed location it is growing in, the more sunlight and the deeper the colour and vice versa.

Pollen morphology
The pollen grains of Disporum taxa of Taiwan are medium-sized monads, monosulcate, prolate, with the length of the equatorial and polar axes being 36.57-44.76 µm and 26.77-28.91 µm, respectively. Sculptural type varies amongst taxa: D. kawakamii and D. sessile var. intermedium are foveolate and areolate, while D. shimadae is rugulate. Huang (1972) studied the pollen morphology of D. kawakamii and D. shimadae by light microscopy and his results showed that the pollen grains of two species were monads, monosulcate, subspheroidal and the sculpture was reticulate. Most of his results are similar to ours, but he sometimes recognised different sculptural types. The different types of microscopy used may lead to the different results ( Fig. 1) ( Table 2).

Distribution
Disporum taxa are found from near sea level to about 2900 m in the mountainous regions of Taiwan, but each species has a different distribution pattern. Disporum kawakamii is found in low to medium altitude mountain areas, often grows as an  Chao et al. 1963;Chang and Hsu 1974;Tamura et al. 1992;Wang 1997 16 Chang and Hsu 1974  north-eastern part, seashore to low altitude mountains understorey plant in a forest or at the edge of a forest, but sometimes even appears on an exposed roadside. Disporum sessile var. intermedium is found primarily at medium altitudes, from 1500 m to 2900 m in moist and shady areas of forest. Disporum shimadae is only found in the north-eastern part of Taiwan, from sea level to low-lying mountains or hills (Table 4) (Figs 2-4).

Evaluation of conservation rank of Disporum
According to a study by the editorial committee of The Red List of Vascular Plants of Taiwan (2017), the conservation rank of D. kawakamii and D. shimadae was least concern (LC), whereas D. nantouense ( = D. sessile var. intermedium) and D. taiwanense ( = D. kawakamii) were data deficient (DD). The results of our study were similar, but we determined that the rank of D. sessile var. intermedium was LC. This was a poorly know taxon, the specimens often being misidentified as another species. During our  field survey, we found many populations at a medium altitude, in good habitats with little disturbance. Therefore, we suggest changing the conservation rank of D. sessile var. intermedium from DD to LC.

Comparison of D. cantoniense and D. kawakamii
Disporum cantoniense is a widely distributed species, found from the Himalayas of northern India to Sikkim, Burma, Thailand, Vietnam and China. Hara (1988) listed four varieties of this species: one of them was D. cantoniense (Lour.) Merr. var. kawakamii (Hayata) Hara. The main characters of this variety include glabrous pedicels, apices of tepals obtuse or short acute and densely papillate (Hara 1988 (Shinwari et al. 1994;Tamura et al. 2013) also revealed that the two species were placed in different clades. In conclusion, D. kawakamii is different from D. cantoniense on morphological, karyological and genetic levels and should be treated as an independent species rather than a variety as Hara (1988) published. Ying (1989) described a new species, D. taiwanense, from eastern Taiwan that was distinguished by its usually reddish petioles and yellow tepals with reddish tips, especially on the inner surface. As we mentioned before, the colour of tepals can vary depending on the habitat conditions; therefore, this character would seem to be a poor one for distinguishing them. Since the distribution of the two taxa is also similar, we chose to consider D. taiwanense as a synonym of D. kawakamii.

The taxonomic status of D. nantouense and D. shimadae
Disporum nantouense has been treated as a form D. sessile var. shimadae f. intermedium (Hara 1988) or as an independent species (Ying 1990a). These treatments were evaluated and considered, but none of them was found suitable for this taxon. The diagnostic characters of this taxon include lanceolate to narrow lanceolate leaves, white tepals, sub-papillose filaments and chromosome number of 2n = 16. These characters are different from those of D. shimadae, therefore, this taxon should not be considered simply as another form of D. sessile as Hara (1988) proposed. These specific characters are, however, found in D. sessile and the molecular study of Tamura et al. (2013) also suggested close affinity between them. Thus, the proposal of Ying (1990a) that this is an independent species lacks sufficient evidence.
Tamura (2016)  The Taiwanese taxon resembled D. sessile var. micranthum in that they both had small flowers (1.5 to 2.2 cm in length) and sub-papillose filaments, but otherwise they were distinguished by the subterranean stolons, lanceolate to nar-row lanceolate leaves and tepals greenish at the apex. Based on the study of Tamura et al. (2013) and Tamura (2016), the Taiwanese taxon was merged into the monophyletic group of D. sessile, with the different morphological characters mentioned above. Thus, we treated this taxon as a variety of D. sessile, rather than a species or a form of D. sessile.
Disporum shimadae was first described by Hayata (1911) as a separate species, but Hara (1988) considered it a variety of D. sessile. Although the two taxa have similar morphological characters, such as leaf shape, long creeping stolons and deciduous habit, D. shimadae could be distinguished by its yellow flowers, thicker leaves and glabrous filaments. Furthermore, as mentioned above, the chromosome number of D. shimadae is 2n = 14, while that of D. sessile is 2n = 16 (Tamura et al. 1992;Wang 1997). This evidence would imply they are not conspecific, similar to the results of the molecular study of (Tamura et al. 2013); consequently, we chose to treat D. shimadae as an independent species, not a variety of D. sessile.

The status of D. taipingense
Another taxon, related to D. sessile var. intermedium, was D. taipingense M. N. Tamura & S. Kawano, nom. nud. This name had been cited in the studies of Tamura et al. (1992) and Shinwari et al. (1994), where they stated that this species was collected from Mt. Taipingshan, at an altitude of 1900 m in a coniferous forest but provided limited morphological description. They cited an article, in press, that could possibly be the original publication of the name (Tamura and Kawano 1994, Biosystematic Studies in Disporum, Liliaceae-Polygonateae V., A Taxonomic Revision of Species in Taiwan in Acta Phytotaxonomica et Geobotanica), but we could not find the article in the journal or the description and the type specimen. Thus, this name is nomen nudum due to its invalid publication. Disporum taipingense was treated as a synonym of D. nantouense in Flora of China . In consideration of the facts that the collectors of the plant had deposited the specimens labelled as D. taipingense by M. N. Tamura in the TI herbarium and the plant materials were from Mt. Taipingshan, but morphological descriptions were inadequate and the "in press" journal article could not be found, we chose to treat this taxon as a synonym of D. sessile var. intermedium.