We talked plenty about this last season, as the Houston Texans prepared to welcome one branch of the Bill Belichick coaching tree. The New England Patriots' leader has had plenty of former assistants move on to head-coaching jobs in both college and professional football.

Erik Frenz of the Boston Globe took a look last week at where things stand. He grouped them in three arboreal parts: the lush, the budding and the barren.

His three lush branches are college coaches: Alabama coach Nick Saban, Iowa coach Kirk Ferentz and Al Groh, who spent nine seasons at Virginia. Among those budding he includes Texans coach Bill O'Brien, who served several roles under Belichick, most recently offensive coordinator.

Since leaving the fold, O'Brien has helped turn things around at Penn State from 2012-2013, and with the Houston Texans where he just served his first year as head coach. The Nittany Lions were coming off the scandal of Jerry Sandusky and the death of Joe Paterno, but O'Brien fought through heavy sanctions to lead Penn State to a 15-9 record in two years. He also turned the Texans from a 2-14 team with the No. 1 overall pick in the 2014 draft, to a 9-7 team despite missing that No. 1 pick (defensive end Jadeveon Clowney) for most of the season.

As Crennel had an incredibly successful season as the Texans' defensive coordinator, Ferentz seems to judge the candidates based on their sustainability as head coaches. He includes Texans defensive coordinator Romeo Crennel in the barren category. He writes: