Luculia

Keys as per Flora of China and As per efi thread:
What struck me is the spathulate calyx given in the description in your book link (at MS,Aug., 2021/08 Luculia sp.for id.) for Luculia pinceana, which I found at Plants from Northeast Tour 2017- Luculia pinceana from Cherrapunji, Meghalaya. Also lamellate appendages at the base of corolla lobes for this species can be seen at Rubiaceae Week: Sharing Rubiaceae Photo from Arunachal Pradesh and A small tree with white flowers and Tohangam,Lohit,Arunachal Pradesh. 3.1.17

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BSI Flora of India Checklist (Distribution):
Luculia gratissima (Wall.) Sweet (Arunachal Pradesh, Assam, Sikkim, West Bengal)
Luculia pinceana Hook. (Arunachal Pradesh, Assam, Meghalaya, Mizoram, Nagaland, West Bengal)

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Flora of Peninsular India with keys at species links, if any:
Luculia grandifolia (Cultivated) (E. Himalaya as per POWO)
Luculia gratissima (Cultivated)
Luculia pinceana (Cultivated)

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Species with distribution in annotated checklist of Flowering plants of Nepal (Distribution):
Luculia gratissima (Wall.) Sweet (1000-2100 m; Himalaya (Nepal to Assam), Tibet, Indo-China, Yunnan)

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Some species found in India with description & keys from Flora of China (Distribution):
Luculia gratissima (Wallich) Sweet (Forests or thickets on mountains; 800-2400 m. Xizang (Mêdog), Yunnan [Bhutan, NE India, Myanmar, Nepal, Thailand, Vietnam])
Luculia pinceana Hooker in Curtis (Forests or thickets on mountain slopes, streamsides in valleys; 600-3000 m. Guangxi, Guizhou, Xizang, Yunnan [India, Myanmar, Nepal, Vietnam])