Which of the following seeds have remained alive for the longest period ?

The correct option is Phoenix dactylifera.

Detailed Explanation:
Seed viability is the ability of a seed to retain its capacity to germinate under favorable conditions. The lifespan of seeds varies dramatically across different plant species; some seeds lose viability within a few weeks, while others can remain dormant and alive for thousands of years.

Among the choices provided, Phoenix dactylifera (commonly known as the date palm) is renowned for its extraordinary seed longevity. During archaeological excavations at King Herod's palace near the Dead Sea (specifically in Masada), archaeologists discovered ancient date palm seeds. Scientists successfully germinated one of these seeds, which was determined to be approximately 2,000 years old. This makes it one of the longest-documented cases of seed viability in scientific records.

Let's look at the other options for comparison:
• Mangifera indica (mango) seeds are recalcitrant, meaning they lose viability very quickly, often within a few weeks of fruit ripening.
• Striga asiatica (witchweed) and Yucca gigantea seeds have typical seed survival lifespans that are significantly shorter, failing to match the archaeological scale of survival demonstrated by the date palm.

Therefore, Phoenix dactylifera is the correct answer as it has remained alive for the longest period among the options listed.