Abstract Aim To explore the effect of Mankai, a cultivated aquatic duckweed green plant, on postprandial glucose (PG) excursions in type 2 diabetes (T2D). Methods In a 4‐week, randomized crossover‐controlled trial, we enrolled 45 adults with T2D (HbA1c range: 6.5%‐8.5%) from two sites in Israel. Participants were randomized to drink Mankai (200 mL of raw‐fresh‐aquatic plant + 100 mL of water, 40 kcal, ~10 g of dry matter equivalent) or water (300 mL) following dinner, for 2 weeks each, with a 4‐day washout interval, without dietary, physical activity or pharmacotherapy alterations. We used continuous glucose monitoring (CGM) devices. Results Forty patients (adherence rate = 88.5%; 743 person‐intervention‐days, 68.9% men, age = 64 years, HbA1c = 6.8%) completed the study with a consistent diet and complete CGM reads. Only two‐thirds of the individuals responded beneficially to Mankai. Overall, Mankai significantly lowered the PG peak by 19.3% (∆peak = 24.3 ± 16.8 vs. 30.1 ± 18.5 mg/dL; P < .001) and delayed the time‐to‐peak by 20.0% (112.5 [interquartile range: 75‐135] vs. 90 [60‐105] min; P < .001) compared with water. The PG incline and decline slopes were shallower following postdinner Mankai (incline slope: 16.8 vs. water: 29.9 mg/[dL h]; P < .001; decline slope: −6.1 vs. water: −7.9 mg/[dL h]; P < .01). Mean postprandial net incremental area‐under‐the‐glucose‐curve was lowered by 20.1% with Mankai compared with water ( P = .03). Results were consistent across several sensitivity and subgroup analyses, including across antidiabetic pharmacotherapy treatment groups. Within 2 weeks, the triglycerides/high‐density lipoprotein cholesterol ratio in the Mankai group (−0.5 ± 1.3) decreased versus water (+0.3 ± 1.5, P = .05). Conclusions Mankai consumption may mitigate the PG response in people with T2D with an ~20% improvement in glycaemic values. These findings provide case‐study evidence for plant‐based treatments in T2D to complement a healthy lifestyle and pharmacotherapy.