The earliest systems of classification used which types of characters?

Explanation

**Step-by-Step Solution:**

1. **Understanding the Question**: The question asks about the types of characters used in the earliest systems of classification of organisms.

2. **Identifying the Earliest Classification**: The earliest classification system was proposed by Carl Linnaeus, which is known as the two-kingdom classification system.

3. **Types of Characters Used**: In this two-kingdom classification, organisms were classified primarily based on:
- **Superficial Structures**: This refers to the external features and appearances of the organisms.
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