PVIK

Polynomial Visual Identification Key (PVIK)

Smart, modern identification app

The Polynomial Visual Identification Key (PVIK) is a modern tool for phytoplankton species identification.

It is based on pairwise classification and coupling – a principle developed by Jerome H. Friedman (1996) and widely used in advanced technologies that use fast identification such as face recognition and autonomous vehicles. This powerful methodology enables PVIK to rapidly narrow down potential species by evaluating multiple morphological features simultaneously.

Developed from over 25 years of professional plankton identification experience, PVIK brings that expertise into an intuitive, efficient digital environment. Although designed for professionals, it can also be used by anyone with the skills needed to distinguish between the groups that the key employs. Species are grouped at the genus level, ensuring clarity and focus.
New groups are added continuously, approximately 15 per year (starting 2026).

Why use PVIK?

Identifying plankton can be challenging: many species look almost identical.
Traditional dichotomous keys are linear and restrictive – forcing you to choose between two options at a time. PVIK changes that. It lets you combine several features at once, making the process faster and much more flexible.

By selecting a group, entering the length and width of the algae you see, and refining with additional features, PVIK quickly produces a shortlist of matching species.

The final verification still relies on standard literature, but PVIK saves valuable time by narrowing the field to just a few likely candidates – while helping you learn and compare species more effectively.

PVIK was initially developed for phytoplankton species, but zooplankton will be included soon.

How PVIK Works

The key currently starts at the genus level. This means that users need basic taxonomic experience – they must already recognize a Closterium or a Phacus. Within each genus, smaller morphological groups are defined based on easily recognizable characters, such as:
– Closterium species with parallel sides
– nearly round Phacus species

Each group typically contains 15-20 species – still challenging, but manageable.
When identifying an unknown alga, the user first selects the appropriate group. The first step is to enter cell length and width. These values are displayed immediately in a size graph showing the ranges of all species in the group. This provides an instant overview of:
– extreme size outliers
– clusters of overlapping species
– where the specimen is positioned relative to others

The user can enter values numerically or place the point directly in the graph with the mouse. While PVIK does not currently contain images or drawings, this visual overview of the sizes is a key advantage – it helps the user understand patterns instead of working blindly through text.
As soon as size is entered, PVIK generates a preliminary candidate list. In a matter of seconds, you move from 20 potential species to perhaps 4 or 5. In traditional keys for Closterium, such as those by Růžička and Coesel, one often has to consider 70 or more species.

Some candidates may appear in a lighter color, indicating that they fall outside the most typical size range of the species. Many groups – especially Closterium – show large natural size variation.
From here, the user can apply 2–5 additional filters simultaneously to further narrow the list – again within seconds. This is the true power of the app. Instead of going back and forth in a dichotomous key you can now just easily choose different features to match your specimen and narrow down the possible species.

The same tools can be used for training purposes, allowing users to explore morphological variation interactively. Just play with the app and learn to see which species have a certain feature and which ones do not. Have fun!.

Get involved

An open version of PVIK with three groups is available to try for free.
Access to the full version (currently seven groups) is available for just 36 € per year (0% VAT) (price for 2026). If you start in the middle of the year, only the remaining months are charged.
Contact us by email to receive your login details.

Would you like to develop a simple identification key for a particular plankton group?
Get in touch – we may be able to create the next PVIK group together.

The app is written by Daniel Blackburn, Startle Company.