A rootstock cannot be a tuber because a tuber is a modified stem.
A variety of terms are applied to storage structures of Dioscorea.
Katherine Esau in her Anatomy of Seed Plants text, Hortus Third,
Webster's New Collegiate Dictionary (under yam) and all the college
introductory botany texts I checked all say Dioscorea has a storage
root or tuberous root. Hortus Third also says D. bulbifera produces
aerial tubers, and some Dioscorea species have rhizomes. A few
websites even claim some Dioscorea species do have corms.
Distinctions between types of modified stems, such as stolons,
rhizomes, tubers and corms, are not always clear cut.
David R. Hershey
"Cereoid+10" <cereoid at prodigy.net> wrote in message news:<flA%9.3109$LZ6.1357 at newssvr16.news.prodigy.com>...
> Sorry Spammy Davis, Jr. but you have already jumped to wrong conclusions and
> that does not help.
>> The rootstock of Dioscorea is a tuber not a corm. A corm is covered by a
> tunic but a tuber is not.
>> Dioscorea is a huge genus and even includes a number of cold hardy species.
>> The "Sweet Potato" Ipomoea batatas is a "Morning Glory" with tuberous roots.
>>> I Don't Like Spam <nobody at ibm.com> wrote in message
> news:1ait3vc1horkuisq67hljgo2v2tia0433s at 4ax.com...> > In article <v3rh869esm5ha5 at corp.supernews.com>,
> > blair <blair863 at hotmail.com> wrote:
> > >I was at somebody's house once and they had a big sprawling plant with
> > >shaped leaves. They said that they grew it by putting a relative of the
> > >family into the ground and planting it. Apparently you could also plant a
> > >yam and grow a different plant as well.
> > >
> > >Does anyone know what this plant is?
> > When I was in college, a friend planted a sweet potato in a pot and
> > let it grow. Later she told her room-mate that it was a "heart-shaped
> > wandering jew". This was believed until an energetic pet knocked the
> > pot over, breaking it, revealing the true nature of the plant. As
> > mentioned earlier, sweet potato is in Convolvulaceae, with morning
> > glories.
> > I wouldn't have brought this up, except sitting on my window sill here
> > at work is a member of the yam family Dioscoreaceae, _Dioscorea
> > macrostachya_, (dormant right now) the leaves of which are very
> > similar to the heart shaped leaves of sweet potato. This grows from a
> > large corm that is quite interesting in appearance. In nature this
> > corm is hidden underground, but when sold as a houseplant, the organ
> > is kept above ground for show (some of the larger, older ones resemble
> > a tortoise shell, at least if you have an active imagination).
> > So, before we jump to conclusions about exactly what the plant is,
> > there ARE some members of the yam family kept as houseplants that fit
> > your description (although, in general, they are a bit pricey, and not
> > very common except perhaps through specialty succulent dealers).
> > Sweet potatoes as sold in the US, often called yams (oh the wonders of
> > misleading common names). Ask your friend if they could allow you to
> > take a look at the underground stem by brusing away a little soil. If
> > it looks like a sweet potato, it probably is. Otherwise, my Dioscorea
> > has a THIN, SINGLE, TOUGH twining vine that comes from the TOP of a
> > CORM-like structure. If I recall correctly, a sweet potato would
> > likely have SEVERAL sprouts coming from a VARIOUS POINTS along a
> > HORIZONTAL TUBER, and those sprouts would tend to be more FLESHY or
> > SUCCULENT, at least close to the tuber.
> > Hope this helps.