Lathraea

Hatt, Sebastian A., Tsiftsis, Spyros & Thorogood, Chris J., 2024, A taxonomic monograph of the Eurasian holoparasitic plant genus Lathraea L. (Orobanchaceae), Phytotaxa 672 (1), pp. 1-29 : 5

Key to the genus Lathraea

1. Flowers arising directly from stem at ground-level ......................................................................................................................... 2

- Flowers borne on a spicate or racemose inflorescence .................................................................................................................... 3

2. Calyx distinctly 4-lobed; corolla 30–90 mm long; c. 4 seeds ...................................................................... 2. Lathraea clandestina

- Calyx unlobed with undulate margin, corolla 19–25 mm long; c. 15–20 seeds .............................................. 5. Lathraea purpurea

3. Inflorescence distinctly unilateral; c. 80 seeds; fruit dehiscing passively ..................................................... 1. Lathraea squamaria

- Inflorescence not unilateral, flowers densely spirally arranged; c. 4 seeds; fruit dehiscing explosively ......................................... 4

4. Inflorescence 200–500(–700) mm tall, bright yellow in fruit; bract 12–14 mm long in fruit; fruit bright yellow; native to Balkan Peninsula .......................................................................................................................................................... 3. Lathraea rhodopea

- Inflorescence 100–300(–400) mm tall; white to cream in fruit; bract 6–9 mm long in fruit; fruit whitish-cream to pale purple; native to China, Japan and Korea................................................................................................................................ 4. Lathraea japonica