Hydrangea lalashanensis S.S.Ying — Lalashan hydrangea

Introduction

Lalashan hydrangea (Hydrangea lalashanensis) is a recently described Taiwanese woody shrub that Tree TSAR provisionally places in Hydrangea subg. Dichroa sect. Chinenses. Shao-shun Ying published the species in 2023 from Lalashan in Taoyuan, northern Taiwan. The 2023 annual review of newly described Chinese plants records the type at approximately 2,150 m elevation and notes that the species was established from morphological evidence; Plants of the World Online currently accepts the species.

The original morphology makes the species unusual. Tree TSAR's morphology-based assessment identified an erect shrub approximately 1.5–2.5 m tall with largely glabrous, narrow lanceolate foliage, enlarged marginal flowers usually bearing three unequal sepals and only rarely four, and a reported four-parted fertile-flower organization including four stamens, four styles, and a four-locular ovary. Those features led us to place the species provisionally in sect. Chinenses, whose H. pottingeri complex similarly commonly bears three or four enlarged marginal sepals.

This placement must remain explicitly provisional. No molecular study located during this review has established the phylogenetic position of H. lalashanensis. More importantly, Yang et al. (2024) demonstrated that the old East Asian chinensis assemblage contains more than one sectional lineage and warned that sects. Chinenses and Kawagoeanae are difficult to distinguish morphologically. Taiwan contains representatives of both evolutionary neighborhoods.

Comparison with the principal sectional alternatives

Character	**Hydrangea lalashanensis**	Hydrangea pottingeri / chinensis concept	**Hydrangea angustipetala**
Working sectional affinity	Chinenses, provisional	Chinenses	Kawagoeanae affinity
Habit	Erect shrub ca. 1.5–2.5 m	Shrub ca. 0.5–4 m	Shrub
Foliage	Narrow-lanceolate; largely glabrous	Variable lanceolate–elliptic foliage; often sparsely pubescent or glabrous	Oblong–lanceolate; pubescent to villose, especially on veins beneath
Enlarged marginal sepals	3, rarely 4	3 or 4	Usually 4
Fertile-flower merosity	Reported 4-merous	Conventional Dichroa pattern	5 sepals and 5 petals
Stamens	Reported 4	8–11	More conventional Hydrangea complement
Styles	4	3–4	3
Ovary	Reported 4-locular	Ca. 1/2 or more superior	Semi-superior
Geography	Lalashan, northern Taiwan	Broad historical East Asian complex	Taiwan
Molecular placement	Unsampled / unresolved	Established Chinenses core	H. macrosepala, synonymized here by POWO but accepted separately by Tree TSAR, sampled within Kawagoeanae lineage

The pottingeri comparison is supported by the traditional H. chinensis diagnosis, which has three or four enlarged marginal sepals, 8–11 stamens, three or four styles, and an ovary about half or more superior. Taiwanese H. angustipetala differs through its more pubescent foliage, four enlarged marginal sepals, five-parted fertile perianth, semi-superior ovary, and three styles. Current Kew treatment accepts H. angustipetala and includes H. macrosepala among its synonyms; Yang et al.'s sampled H. macrosepala belongs to the lineage they recognized as sect. Kawagoeanae.

The comparison explains why Tree TSAR presently favors Chinenses: the three, occasionally four, enlarged marginal sepals align more closely with the pottingeri/chinensis morphology than with the usual four or five enlarged sepals diagnosed for Kawagoeanae. The earlier Tree TSAR assessment likewise identified this character combination as the strongest practical reason for a provisional Chinenses placement. Geography alone cannot resolve the issue.

The reported four stamens are more problematic. Yang et al. characterize subg. Dichroa generally by 8–12 stamens, rarely as many as 20. If four stamens prove constant in normal fertile flowers of H. lalashanensis, the species would possess an unusually reduced androecium requiring more careful evolutionary interpretation. Tree TSAR therefore treats this character as a specific verification target rather than using it by itself to remove the species from subg. Dichroa. Examination of additional flowers and the type material is needed to determine whether the count is stable.

Two NTUF sheets, NTUF-112-043 and NTUF-112-044, are explicitly catalogued under H. lalashanensis. These provide an obvious starting point for any future morphological reassessment.

The present Tree TSAR classification is consequently:

Subgenus Dichroa → Section Chinenses → Hydrangea lalashanensis,

with moderate-low confidence at sectional level but normal acceptance at species rank. This preserves the morphology-based working conclusion while keeping the sectional placement explicitly provisional.

Horticultural and Agricultural Uses

The species is too recently described for a meaningful horticultural tradition to have developed, and no authenticated cultivar history or widespread commercial material was located.

Its compact shrubby habit, narrow foliage, and high-elevation Taiwanese origin could eventually make it attractive to specialist Hydrangea collections. For the moment, however, its greater horticultural value is scientific. Living material collected under permit with precise provenance would allow direct verification of the unusual floral structure and provide tissue for the molecular work necessary to establish sectional placement.

No agricultural or medicinal use is documented.

Conservation Concerns

No formal IUCN Red List assessment was located. Hydrangea lalashanensis was described only in 2023 from Taoyuan, Taiwan, with the cited type locality at approximately 2,150 m. Current information is therefore inadequate for reliable inference about abundance, population number, or range extent.

Its apparently localized montane occurrence makes field documentation worthwhile, but rarity should not be inferred merely from the recent date of description. Surveys should first determine whether the species is genuinely restricted to the Lalashan region or has been overlooked elsewhere among superficially similar Taiwanese hydrangeas.

Conservation and systematics are unusually intertwined here. Verified populations could simultaneously establish geographic range, test the stability of the diagnostic morphology, and provide the first molecular evidence distinguishing a Chinenses placement from a Kawagoeanae placement.

Additional Information

Plants of the World Online — Hydrangea genus record including H. lalashanensis (opens in a new tab)

Taiwan NTUF type-sheet catalogue (opens in a new tab)

iNaturalist search — Hydrangea lalashanensis (opens in a new tab)

References and Further Reading

Du C, Liu J, Ye W, Liao S (2024) 2023 annual report on new taxa and nomenclatural changes for Chinese plants. Biodiversity Science 32(11): 24253. https://doi.org/10.17520/biods.2024253 (opens in a new tab)

[Records Hydrangea lalashanensis as a morphology-based new species from Taoyuan, Taiwan.]

Yang X, Xue T, Gao T, Liang Y, Smets EF, Gadagkar SR, Yu S (2024) An updated infrageneric classification based on phylogenomics and character evolution in Hydrangea (Hydrangeaceae). Taxon 73(2): 503–518. https://doi.org/10.1002/tax.13158 (opens in a new tab)

Ying SS (2023) Two species of genus Hydrangea (Hydrangeaceae) in Taiwan. In: New taxa & new names, vol. 6. Research Center of Flora of Taiwan, Taipei, pp. 164–177. https://homepage.ntu.edu.tw/~yingshao/NEW%20TAXA%20%26%20NEW%20NAMES%2C%20vol%206-1.pdf (opens in a new tab)