Re-appraisal of Nertera (Rubiaceae) in Taiwan

Abstract A revision of Nertera (Rubiaceae) in Taiwan was carried out by classical taxonomic methods and the presence of two endemic species was confirmed. Only one species, misapplied as N.granadensis, had been reported in the second edition of “Flora of Taiwan”, but there were two additional endemic species in this genus: N.nigricarpa and N.taiwaniana confirmed. Nerteranigricarpa is characterised by the entire leaf, purple-black petals, black fruits and dark-purple seeds with raised striate. Nerterataiwaniana has leaves with undulated margins, yellowish-green petals, red fruits and yellow-white seeds without striate. N.granadensis is excluded from the flora of this Island.


Introduction
There are six known species in the genus Nertera Banks ex Gaertn. in the family Rubiaceae in Australia, New Zealand, South America, Indonesia (Java), China, Taiwan and the Philippines (Chen and Taylor 2011). Moreover, Thompson (2010) suggested about 15 species in the genus. Hayata (1908) first described N. nigricarpa Hayata and reported that it is endemic to Taiwan and distributed at mid-to high-altitudes across the Island. Later, Hayata (1918) provided line drawings of N. nigricarpa. Masamune (1938) first described N. taiwaniana Masam., which has red fruits and was only known from the Jingshueiying area in southern Taiwan. However, N. taiwaniana has recently been discovered near Yuanyang Lake in northern Taiwan and at Lijia Industry Road in eastern Taiwan. Yamamoto (1938Yamamoto ( , 1940 believed that N. depressa Banks & Sol. ex Gaertn. in the Philippines and N. taiwaniana in Taiwan were the same species. Chao (1978) included both N. depressa and N. nigricarpa in the first edition of "Flora of Taiwan" and also treated N. taiwaniana as being a synonym of N. depressa in accordance with Yamamoto (1938Yamamoto ( , 1940, which was followed by . Liu and Yang (1998) only recorded one species, N. granadensis (Mutis ex L. f.) Druce, in the second edition of "Flora of Taiwan" and treated N. depressa and N. nigricarpa as synonymous.

Materials and methods
This study is based on field observations and detailed examinations of herbarium specimens. Specimens examined included those from the Herbaria CHIA, HAST, TAI, TAIF and TCF. The other type specimens were accessed as digital images of Nertera depressa and N. granadensis from Herbaria LINN and WELT. Morphological comparisons of fresh leaves, flowers, fruits and seeds were observed and stereomicroscopic pictures were taken of plants from Taiwan. Their sizes were measured by a digital caliper.

Results and discussion
Based on field observations and detailed examinations, we verified that the black-fruited Nertera and the red-fruited Nertera, native to Taiwan, are different species (Fig. 1). Nertera taiwaniana has leaves with undulating margins and secondary veins that are distinctly convex on the upper surface, yellowish-green petals, red fruits and yellowwhite seeds without striate surfaces. Nertera nigricarpa is characterised by leaves entire without undulating margins and secondary veins which are not apparent on the upper surface or, if apparent, then only slightly convex, purple-black petals, black fruits and dark-purple seeds with raised striate.
Furthermore, after studying the lectotypes of Nertera granadensis (Mutis s.n., LINN) and a live individual, growing in its country of origin, Columbia, we found that the leaves of N. granadensis are nearly fleshy, with no apparent veins on both surfaces, without undulating margins, with an obtuse to acute apex and obtuse to shallowly truncate base and with red fruits that have no black spots. Therefore, N. granadensis is morphologically distinguishable from N. nigricarpa and N. taiwaniana. Although, the fruits of both N. granadensis and N. taiwaniana are red, N. taiwaniana possesses leaves that are membranous to papery with distinctly convex veins, an acute apex, a cordate or truncate base and fruits with black spots.
Nertera granadensis has often been referred to as N. depressa Banks & Sol. ex Gaertn, the type of the genus (Chen and Taylor 2011). Chao (1978) treated Nertera taiwaniana as a synonym of N. depressa. We also compared at syntype of N. depressa (Banks & Solander s.n., WELT SP063852). Nertera depressa possesses slightly fleshy leaves with no apparent veins, no undulated margins, an acute apex, an obtuse or shallowly cordate base and fruits that are red without black spots. In particular, the top hollow of N. depressa's fruit is black. This characteristic is never found on the species native to Taiwan and N. granadensis.
Considering the current evidence, the endemic species, N. nigricarpa and N. taiwaniana were proposed herein readily distinguished from N. granadensis and N. depressa.