Detecting Central Axis (petiole/rachis) of a Pinnated Palm I'm new in StackExchange and I'd appreciate some help. I'm working in an algorithm for detecting "aguajes", a particular kind of palm. So far, I got good results using a texture feature extractor and other characteristics, but the main problem is that I can't difference between an "aguaje" and other palms (mainly pinnated palms) because the texture is very similar. 

1.AGUAJE


2.Pinnated Palm


I see that the main difference in the second one is the presence of a Central Axis (also called Petiole or Rachis). The question is "How to detect it?". I mean, if I'm able to detect the presence of a Petiole, I'd be able to distinguish between this two types of palm. I think color is not an important issue because even when there's no color (gray image), we can discern where is located that Axis.

Thanks in advance.
In your provided image the central axis is straight and have the same color throughout, therefore a Hough operator can detect this.