Abstract. This study was aimed to know the effect of water-extracted shrub Clerodendrum minahassae L. leaf application on the growth of algae Nannochloropsis sp. It used Complete Randomized Design with 4 treatments of the shrub concentrations, 2%, 4%, 6%, 8% of total water volume of Nannochloropsis sp. culture, positive control, and negative control, each of which with 3 replications. The culture media was water-extracted shrub C. minahassae leaf, whereas the positive control treatment used Walne fertilizer. Negative control treatment was also prepared without addition of Walne fertilizer or the shrub leaf fertilizer. Nannochloropsis sp. was cultured in the glass jar containing 1 L of water. Results showed that the highest growth of Nannochloropsis at 4% shrub extract concentration was 82.3×107±4.7×107 cells in day-4, and 6% shrub extract concentration yielded the highest density in day-3, 70.7×107±19.0×107 cells, whereas the concentration of 2%, 8%, positive control, and negative control had low cell density and quickly declined then began to die in day-4 to day-9. This finding concluded that addition of the shrub leaf concentration significantly influenced the density of Nannochloropsis sp. (p < 0.05), in which the addition of 4% and 6% shrub leaf extract concentration was the best treatment to yield the highest density of Nannochloropsis sp. cells.

Key Words: water-extracted shrub, glass jar, plant fertilizer, density, alga.