I apologize if my interest for the best up to date answer to the question of Manfreda as a genus (yes or no) might be getting to be a bore. For me, truth and knowledge are not boring, and it's well worthwhile.
I've seen that elsewhere in Internetlandia, this discussion has been referenced, and additionally characterized as "chatter".
At least according to the meaning of the word as I understand it, that was obviously not intended in any complementary way. OK, whatever.
I've been digging furiously for more information on the actual evidence where people say DNA indicates Manfreda is not a genus of it's own. Sure, there are opinions aplenty. What I'm looking for is fact, based on the actual scientific studies of molecular data referenced. I can't find more than what's been already mentioned, that is current and relevant. The most current study I'm aware of incorporating molecular data for classification is the "PHYLOGENY OF AGAVACEAE BASED ON"... (Bogler, et al. 2005) for which I already provided the link previously.
1. Data for only Manfreda virginica has been considered, according to Table 1.
2. "Manfreda virginica was not resolved from Agave in this analysis..." page 10
3. The tree illustrated on page 6 indicates a Bootstrap Support Value of 72 at the node where Manfreda is listed.
So where is the evidence whereby one can eliminate Manfreda as a genus?
After some research, I can capsulize that values close to 100 are considered well supported. 72 is considered "moderate". I fail to understand how one interprets moderate as certain. Furthermore, when one investigates this concept, you will find:
"Evolutionary trees are often estimated from DNA or RNA sequence data." Key word: ESTIMATED
"The bootstrap ... is a computer-based technique for assessing the accuracy of almost any statistical estimate." We're talking statistics, and probabilities. NOT certainties....difference.
Here's a good simplification/explanation I found offered by someone from the University of Vermont:
"Bootstrapping is a resampling analysis that involves taking columns of characters out of your analysis, rebuilding the tree, and testing if the same nodes are recovered. This is done through many iterations. If, for example, you recover the same node through 95 of 100 iterations of taking out one character and resampling your tree, then you have a good idea that the node is well supported. If you get low support, that suggests that only a few characters support that node, as removing characters at random from your matrix leads to a different reconstruction of that node. ....I would suggest that a maximum likelihood tree with bootstrap values of 70% throughout would probably not go over well with reviewers."
So, it's very important that one looks at a tree diagram, one must be mindful that we are looking at probabilities, likelihoods, and estimates.
http://statweb.stanford.edu/~susan/papers/bootss5.pdf" onclick="window.open(this.href);return false;
I have just a bit more chatter in conclusion.
Here's an abstract published in 2012.
Mexican Geophytes I. The Genus Polianthes.
http://www.liliumbreeding.nl/FOB_6(SI1" onclick="window.open(this.href);return false;)122-128o.pdf
"The genus Agave L with a c. 166 species is the largest genus in the family Agavaceae,
a family that contains 9 genera and c. 293 species (Eguiarte et al. 2000). The genus Agave is paraphyletic to the
genera Manfreda Salisb., Polianthes L. and Prochyanthes S. Watson, and the entire clade comprising the 208 species that belong in the four genera has been termed Agave sensu lato (Eguiarte et al. 2000). The genus Agave sensu stricto is predominantly monocarpic and harbors the most dry-adapted (and succulent) members of the family Agavaceae (Good-Avila et al. 2006). It is divided into two subgenera, Liattaea (53 species) and Agave (113 species) based on the inflorscence (Gentry 1982).
The three genera that are additionally included in Agave sensu lato, Manfreda, Polianthes and Prochnyanthes are predominantly polycarpic, herbadeous, and inhavit a more temperate environment."
It would appear that not everyone, even folks publishing abstracts, yea...even in these modern times, are on board with the reclassification which supposedly makes "Manfreda" obsolete. Now, why is that?