The 30-year-old seamer joins the county as an overseas player following his departure from Glamorgan
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Marchant de Lange has signed a two-year contract with Somerset.
The 30-year-old seamer joins the county as an overseas player following his departure from Glamorgan, where he had not been registered as a local player by virtue of his wife's UK passport.
He will be available to Somerset in all forms of cricket in the 2021 and 2022 seasons.
The county's director of cricket, Andy Hurry, said: "Marchant will no doubt add real value, a different dimension to an already potent bowling attack and demonstrates our intent to continue to strive to winning silverware."
"Marchant's skill, experience and ability to bowl at express pace will complement our bowling group perfectly. He has the proven ability to take wickets and positively change and influence games across all formats and I believe he will be a great fit for our environment."
De Lange, who was left to look for an overseas deal in county cricket from 2021 owing to rule changes brought about by Brexit, said: "It is a huge privilege for me to be joining Somerset and I can’t wait to start my journey with such an ambitious and proud club.
"I am very excited of the prospect of being part of a formidable team and striving towards winning multiple competitions and silverware. It is very noticeable how well supported the club is and I am really looking forward to meeting the members and supporters hopefully on their safe return in 2021."