Under the Settings button menu, many particle types can be selected, most of which correspond to different plants, such as Aloe, Dog Willow and Lichen. Paint with any of these, and the design really does approximate the plant. It seems to save a lot of time over painting each stalk and flower individually.
Other than particles, there's also a bristles tab, which approximates brushing with the bristles of a paintbrush. Many different bristle styles can be selected. Neither particles and brushes need be preset: There are sliders and values that can be tweaked for each one. New plant formations are discovered this way.
One repeatable crash bug occurs whenever the "Nova" style is selected. A runtime error occurs and the program closes. This style needs be disabled in the current version until it works correctly.
Even if you're not a serious artist, this is worth a download just to mess around with--just avoid the Nova style until the bug is fixed.
Note: This link takes you to the vendor's site, where you can securely download the latest version of the software and some free plug-ins. However, the all-purpose paint program Project Dogwaffle, available as freeware from TheBest3D.com, includes particle-based painting. It's not as advanced as what you'll find in PD Particles, but it gives you an idea of how PD Particles works.