I will go over the longer text you sent shortly. In the meantime, it may help to conceive of the petiole as originating from the stem. The stem can be a twig on an oak tree or it can be a rhizome, etc. In Zamioculcas, as far as I can tell, the rhizome is tuberous (or tuberously thickened) and is similar to the rootstock of Gonatopus. In both cases the rhizome is irregularly tuberous or swollen and ultimately the plant forms a compact clump with multiple growing points. However, the roots are not tuberous-- the "tuberousness" is in the rhizome. Plants with more orthodox tuberous roots include Dahlia, Chlorophytum and others.Â
Applying these concepts and terms is relatively straightforward in some cases but every form "in between" also occurs and it becomes very problematic to employ a precise terminology for rootstocks. I read a paper years ago describing the "tuber" of a Dioscorea and they described it as having features of both root and stem at the anatomical level!
Thanks Susan, that and quite a few other changes have now been
made to the page as a result of information that was kindly
provided by Dylan Hannon at the Huntington.Â
The petiole grows from a unique structure beneath
the soil known as tuberous rhizome roots.Â Tuberous roots
are true root tissue that is swollen possessing tuberous
portions that radiate from a central point known as a crown.Â
The crown serves as the growth point for the petiole and is
effectively the stem.Â The petiole changes to become the rachis
(RAY-kis) at the point where the leaflets begin to grow creating a
single compound leaf so Marek, you had it correct.
Thanks to all that offered help but a special thanks to Dylan for
his time today!Â If anyone spots an editing error anywhere on the
site feel free to point it out.
I have a kind lady that tries to find all my errors and we are
having the entire page checked now for typos now but we can always
use the help from growers on this forum!Â I can tell you for
certain, there is a ton of bad information on the internet about
this plant species!
I can only guess that they
call rhachis the part of theÂleaf with leaflets, as they
describe that the petiole is 15-35 cm long. My plant's
total leaf length is up to 120 cm. So possibly the
petiole is the thick part without leaflets and the
rhachis is the rest of the leaf.
I addressed this to Anna Haigh at the Kew but I welcome
input from anyone familiar with this plant.Â I continue to
receive mail from folks telling me the page is wrong no
matter how I describe the central stalk that supports the
leaflets which are on short petiolules.
Anna, can you pass this along to someone that can give me
an accurate answer?
I have revised my page on Zamioculcas zamiifolia several
times over whether or not the plant's central stalk is a
petiole or a or a rachis and the leaflets are
petiolulate.Â I found this on cate this morning and it
appears it has both but I can't discern which is which.Â
Tuber subcylindric, Â 3-4 cm. in
diameter or more, tough, woody. LEAVES: Petiole
green with darker transverse blotches, 15-35 cm. long,
1-2 cm. in diameter near base; blade 20-40 cm. long;
leaflets 4-8 per side, subopposite, distant,
oblong-ovate to -elliptic to -obovate, sometimes
oblanceolate, fleshy, dark glossy green, 5-15 cm.
long, 1.5-5 cm. broad, shortly acuminate, sessile or
shortly petiolulate, articulated to rhachis, cuneate
to rounded basally; rhachis terete, marked like
Will you take a look at the page or ask someone that is
knowledgeable about the plant to tell me exactly where the
rachis and petiole differ?
All the rest of the material was taken from Pete, Simon
and Josef's text The Genera of Araceaa and despite the
fact growers argue with me all the time I will take their
word over that of any grower that believes this plant
should b grown dry.Â It does grow in dry conditions part
of the year, but it is not a desert species!