A giant “tequila plant” is set to flower for the first – and only – time after more than half a century.
The flower spike appeared a month ago at Cambridge University Botanic Garden and is now three metres (10ft) tall.
Staff have been tending the agave, part of a family of plants from which tequila is made, since 1962 but cannot confirm its species until it flowers.
They will soon have to remove the roof of the glasshouse as it continues to grow, but once it flowers, it will die.
Experts at the garden were delighted when the plant’s spike began to grow, indicating it will finally bloom.
The succulent resembles a giant asparagus spear and is related to the vegetable as a member of the Asparagaceae family.
It is not known how tall it will grow to but plans are in place to remove panes from the arid house roof so it can continue its upwards journey.
Agaves are monocarpic, which means they only flower once, set seed and then die.
Although staff believe it might be the species Agave heteracantha, they cannot be sure until they see what sort of flower it finally produces – and they think it could take another month before it blooms.
Sally Petitt, head of horticulture at the garden, said: “It’s very exciting for us – it was sitting there quite quietly and then all of a sudden this happened.”
Once an agave plant dies, it sometimes produces new rosettes at the base, and she hopes this one will do the same “so that some part of it will remain”.
Two years ago a Devon homeowner was equally surprised when her agave shot up 9m (30ft) and flowered after lying dormant for 20 years.