Carpinus gigabracteatus Z. Qiang Lu, 2020

Lu, Zhiqiang, 2020, Carpinus gigabracteatus, a new species from southeast Yunnan, China, PhytoKeys 145, pp. 47-56 : 47

Carpinus gigabracteatus Z. Qiang Lu sp. nov. Figures 1 , 2 大苞鹅耳枥

Diagnosis.

Carpinus gigabracteatus differs from C. tsaiana by leaf length to width ratio 1.4-2.0 (compared to 2.0-2.4), lateral veins impressed adaxially, 9-14 lateral veins on each side of the midvein (compared to 14-18), bract length 3.9-4.8 cm (compared to 2.5-3.0 cm) and bract length to width ratio 2.3-3.1 (compared to 1.5-2.1).

Type.

China. Yunnan: Wenshan Prefecture, 23°09'35"N, 104°05'53"E, 1591 m alt., karst limestone hill, 23 Sep 2019, Z.Q. Lu 2019GY0801 (holotype, HITBC; isotypes, HITBC and LZU).

Description.

Tree to 8 m tall, deciduous; bark grey, smooth. Branchlets black-brown, glabrescent. Petiole 7-14 mm, densely yellow pubescent when young, glabrescent in the following few months; leaves alternate, leaf blade elliptic, ovate-elliptic or ovate, usually 7-12 × 4-7 cm, length to width ratio 1.4-2.0, leathery, abaxially sericeous-villous or sparsely villous along veins, bearded in axils of lateral veins, adaxially densely villous when young, base rounded, rounded-cuneate or cordate, margin regularly or irregularly and doubly minutely serrate, apex acuminate; lateral veins 9-14 on each side of midvein, raised abaxially, significantly impressed adaxially. Male inflorescence pendulous, spicate-cymose, cylindrical, enclosed by buds during winter, with many overlapping bracts, 1.0-3.0 × 0.4-0.6 cm when mature; flowers without bracteoles, inserted at base of bracts. Female inflorescence terminal or axillary on dwarf shoots, racemose; flowers paired; bracts leaf-like, complanate, overlapping. Mature infructescence 8.0-12.0 × 5.0-5.5 cm; peduncle 1.5-2.5 cm, densely yellow hirsute; giant bracts loosely overlapping, 3.9-4.8 × 1.4-1.8 cm, abaxially densely yellow hirsute along reticulate veins, outer margin coarsely dentate and rarely entire, commonly without but sometimes with basal lobe, inner margin entire, with inflexed basal auricle, apex acuminate; veins 5-6. Nutlet ovoid-ellipsoid, 5.3-7.0 × 4.0-5.5 mm, densely pubescent, densely villous at apex, densely brown resinous glandular, prominently 9 or 11-ribbed.

Etymology.

This hornbeam from southeast Yunnan has extremely large bracts, which are distinctly different from other closely related hornbeams, and therefore is given the epithet gigabracteatus .

Phenology.

Flowering from April to May and fruiting from July to September.

Habitat, distribution and conservation.

Up to now, only one C. gigabracteatus population has been collected from southeast Yunnan. For its population census, only six mature trees (6-8 m in height) and 13 seedlings grow on a steep karst limestone hill. To the present author’s knowledge, the bract size of this species is now the largest across the whole hornbeam genus in China. Hence, it has great horticultural and ornamental value and some people like to dig them up to grow them as ornamental trees. Manual digging involves removing lots of large rocks on the limestone hill where this new species grows, resulting in significant damage to the habitat. So far, no other population has been found, even though multiple rounds of field surveys in Wenshan Prefecture and adjacent regions have been carried out in the years from 2013 to 2019. Therefore, this hornbeam is exposed to significant threats from human activity due to its rarity and horticultural and ornamental value. According to the IUCN Categories and Criteria ( IUCN 2016), the present author here classifies this species as "Critically Endangered" (CR). Fortunately, these mature trees can provide the possibility to expand population based on seeds.

Additional specimens examined.

China. Yunnan: Wenshan Prefecture, 23°09'35"N, 104°05'53"E, 1591 m alt., karst limestone hill, 23 Sep 2019, Z.Q. Lu 2019GY0802; the same locality, 10 July 2019, Z.Q. Lu 20189801-Z.Q. Lu 20189804.

Figures

Figure 1. Carpinus gigabracteatus Z. Qiang Lu A the whole plant, habitat and location B branches with infructescences and leaves C infructescences D leaf E bracts F nutlet.

Figure 2. Carpinus gigabracteatus Z. Qiang Lu was drawn from Z. Q. Lu 2019 GY 0801 (HITBC).