Two new taxa of Gesneriaceae in the karst regions in North Vietnam

Abstract One new species and one new variety of Gesneriaceae in Vietnam are described, viz. Paraboea sinensis var. glabrissimavar. nov. and Primulina xuansonensissp. nov. These two new taxa grow in limestone regions in North Vietnam. The former new variety differs from Paraboea sinensis (Oliv.) Burtt var. sinensis in its young leaf abaxially, stem and peduncle sparsely and thin pannose, acute top of leaves, pistil glandular-pubescent or pubescent. The latter new species differs in its bracts 1.6–2.5 × 1.3–1.5 cm, corolla 3–3.5 cm long, corolla tube slightly curved near the base and inflated on the adaxial surface near the corolla lobes, and corolla abaxial lip lobes rounded. The two new taxa grow at Xuan Son National Natural Reserve, North Vietnam and remain undisturbed with low risk of extinction.

Many species of Gesneriaceae are distributed both in South China and in North Vietnam. China is a significant centre of diversity of the family Gesneriaceae, with the majority of taxa found in the South and Southwest China (Wang et al. 1990(Wang et al. , 1998Li 1991Li , 2005Wei et al. 2010;Möller et al. 2016). After long-term collaborative surveys between China and Vietnam, we not only confirmed the common species and records from two countries, but also published some new species endemic to Vietnam, especially in the adjacent region to South China (Chen et al. , 2018a(Chen et al. , 2018b. Here, we describe two new taxa of Gesneriaceae in the karst regions at Xuan Son National Park in North Vietnam (Fig. 1)

Materials and method
After reviewing preserved herbarium specimens worldwide (BM, E, HNU, K, KUN, P, PE), two new taxa were confirmed. Habitat photographs and images of macromorphological characters were taken in the field, in greenhouses and from the fixed (FAA) material. Morphological observations and measurements of the new taxa, based on living and dry plant specimens (from KUN) and preserved materials, were carried out. All morphological characters were observed and photographed with a Leica S8 APO stereomicroscope and a Nikon D700 microscope camera. Diagnosis. The new variety is similar to Paraboea sinensis (Oliv.) Burtt var. sinensis in its morphology of habit, calyx, corolla and fruits, but differs in its young leaf abaxially, stem and peduncle sparsely and thin pannose (vs. dense and thick pannose), acute top of leaves (vs. acuminate), pistil glandular-pubescent or pubescent (vs. glabrous).

Primulina xuansonensis
Phenology. Flowering from October to December, fruiting from December to January from cultivated plants.
Etymology. The name refers to the type locality. Distribution and habitat. The new species only grows in the limestone forests' rock crevices and distributes in the type locality, Xuan Son National Park of Pho Tho Province, North Vietnam.
Provisional conservation status. We observed it in the field with very few individuals (about ten individuals). Due to the similarity of plants without flowers in the genus Primulina, we did not pay attention to the species in the field, so the number of mature individuals remains unknown. Provisionally, it is best to consider it as Data Deficient (DD) ( Wang et al. 1998;Wei et al. 2010;Pan et al. 2013;Shui et al. 2017;Wen et al. 2019). Within the above complex, the new species is different from all the others in its white throat out-side the corolla, except for P. lungzhouensis. Furthermore, the new species is different from P. lungzhouensis in its bracts 1.6-2.5 × 1.3-1.5 cm, corolla 3-3.5 cm long, corolla tube slightly curved near the base, inflated on the adaxial surface near the corolla lobes and corolla abaxial lip lobes rounded. P. lungzhouensis, however, has bracts 2.5-3.8 × 2.2-2.8 cm, corolla 4.5-5 cm long, corolla tube not curved, not inflated on the adaxial surface near the corolla lobes and corolla abaxial lip lobes triangular. In a word, the new species is unique in its narrow and curved corolla tube amongst the above complex with prominent bracts (Table 2).