Extending/Extended

[piggy386]

Scientists have recently discovered what could be the largest and oldest living organism on Earth, a giant fungus that is an interwoven filigree of mushrooms and rootlike tentacles spawned by a single fertilized spore some 10,000 years ago and extending for more than 30 acres in the soil of a Michigan forest.

The official answer is "extending"
To preserve parallelism, I thought the answer should be "extended."
spawned...extended...

Can anyone tell me why the use of "extending" is grammatical correct in this sentence?
Thanks.

[Temico]

Scientists have recently discovered what could be the largest and oldest living organism on Earth, a giant fungus that is an interwoven filigree of mushrooms and rootlike tentacles spawned by a single fertilized spore some 10,000 years ago and extending for more than 30 acres in the soil of a Michigan forest.

It will be easier to comprehend if you read it like this:-

"Scientists have recently discovered........a giant fungus.... (which was)spawned by a single fertilized spore some 10,000 years ago and (is)extending for more than 30 acres in the soil of a Michigan forest."

The use of "(is)extending" is because the giant fungus is still alive.

[piggy386]

It will be easier to comprehend if you read it like this:-

"Scientists have recently discovered........a giant fungus.... (which was)spawned by a single fertilized spore some 10,000 years ago and (is)extending for more than 30 acres in the soil of a Michigan forest."

The use of "(is)extending" is because the giant fungus is still alive.

Thanks, Temico.
I think I probably got your idea...
When we reduce a verb to its -ing or -ed form, we must look at one and only one thing: whether the noun that it will modify is the subject or object of that verb.
The -ing form is used for DOING the action, which means SUBJECT, which means ACTIVE voice.
The -ed form is used for RECEIVING the action, which means OBJECT, which means PASSIVE voice.

[Temico]

I guess the reason why nobody answers your questions is .......you tend to jump to unfounded conclusions!!