Small yellow flowers opened on stems peeking from heart-shaped floating leaves on the water. At Ninomaru Pond in the East Gardens just south of Palaceside Building in Takebashi, Tokyo, blooms began among water-shield leaves covering about half the pond — coloring early-summer water sooner than water lilies or lotus; from the shore the view now splits with purple irises.
Water shield reproduces by seed and by broken stems rooting anew. Seeds survive years in bottom mud; they germinate when water drops in spring and the bottom is exposed. Rising water lets long petioles adapt, but sudden rises weaken and shrink populations. Once common at Kasumigaura, habitat loss and sustained high water from management caused sharp decline — listed endangered (Category II) in the Environment Ministry Red Data Book.
Around Kasumigaura, citizens, municipalities, and elementary pupils joined conservation: adding soil for shallows, stopping high-water management, replanting water shield — temporary recovery; in 2007 the book downgraded it to near-threatened.
The Imperial Household Agency says East Gardens Ninomaru water shield is not from Kasumigaura but propagated from plants in the Fukiage Gardens pond inside the palace — Edo-native water shield.