Papyrus is known to grow on the Nile. It appears between 50 and 200 coordinates north of the location the seeds are placed in the Nile (on both sides), and once it begins to appear grows quickly. Each plant produces a single unit of papyrus. Papyrus takes about 10-15 minutes to grow after planting.
During beta, Teppy mentioned that there were certain "receptors" where papyrus would grow once cast, so it seems there are optimal places for growing, and there are possibly dead zones.
We have a map Papyrus Spots to track good spots to plant Papyrus, so if you know some please add it.
Like flax, papyrus seeds are consumed when planted, so it important to know how to produce more seeds as your supply dwindles. Certainly, drying papyrus sometimes produces seeds. Drying at high altitudes produces more seeds, as a general trend.
It can be dried in a Drying Rack which takes around 20 Teppy minutes.
Using a Flax hammock takes 4 Teppy minutes to dry.
Temperature/time of day, and random chance, may also affect the number of seeds.
Papyrus seeds are marked "(hf)", which stands for "handfuls".
I have obtained 2.5 - 3.2 x yields in Lower Nubia in the mountains SW of the big lake. Time was around 2:00 PM - DysonFeynman
LN near 483 -4482: 68 seeds for 20 papy on a high mountain at 4PM - Roen
My best yields to date 7.2, directly West from RSO center. 25 hf, 50 coord North of the Old UBod bridge, one hf every 10 coords heading N. - Pheanor-Re
Yield so far 7.85 near karnak , used 20 seeds (1 every 10 coors heading south) and got 157 papyrus - gspusi 8.3 yield this time near karnak , used 30 seeds (1 every 8 coors heading south) and got 251 papyrus - gspusi
I have tossed in 9 seed(hf) and came out with 122 papyrus - 13.55 per, by tossing them at the bridge south of 1462, 2196 (west of red sea oasis), at about 3 coordinates appart, then working up to this location. This was at 11:30pm Akhet II-20 - LithFael