100 
KATHY M. NICHOLS, J. H. BROWNE AND R. F. PARSONS 
roots in a number of layered, horizontal planes 
(Fig. 8A). Lateral tuberous roots were seen from 
100 to 500 mm below the soil surface; vertical 
tuberous roots continued beyond 750 mm. 
Tuberous roots are common in a number of 
liane families including the Asclepiadaceae, es¬ 
pecially in species from seasonally dry areas 
rather than those from undisturbed evergreen 
rainforest (Hegarty 1989, Janzen 1975). Ascle- 
piad examples include various African species of 
the succulent genus Ceropegia (Jacobsen 1960) 
and the Australian Marsdenia Jlavescens, M. lep- 
tophylla and M. viridiflora (Williams 1984). 
Excavation of three small Rhyncharrhena 
shoots in an area of 500 x 200 mm showed them 
to be suckers, again from lateral roots (proved by 
tissue sections). Unlike Marsdenia, Rhynchar¬ 
rhena roots are thin (diameter rarely greater 
than 5 mm) and non-tuberous, the laterals are 
not found deeper than about 200 mm and there 
is little branching (Fig. 8D). Starch grains are 
absent from the roots but present in the stems as 
before. Lines of sucker shoots strongly suggest 
that lateral roots can extend more than 15 m 
from parent plants (Fig. 9). 
Root suckering, recorded here in Marsdenia 
and Rhyncharrhena , is known in other 
asclepiads, e.g. in Morrenia odorata (Tucker & 
Phillips 1974) and Asclepias syriaca (Bhowmik 
& Bandeen 1976) which can form clones of sev¬ 
eral thousand stems (Wilbur 1976). Such suck¬ 
ering may be “the most conspicuous form of 
asexual multiplication” in tropical perennials 
and may, for all we know, produce very large 
individual plants of great longevity, each spread 
over many hectares (Janzen 1975). Such sucker¬ 
ing may allow some liane individuals, including 
Marsdenia laxijlora , to persist more or less in¬ 
definitely in the absence of regeneration from 
seed (Penalosa 1984). Other aspects of suckering 
are dealt with later. 
Without data on root depth limits and lo¬ 
cation of soil moisture reserves, we are unable to 
classify Marsdenia and Rhyncharrhena root 
systems into types. Clearly both have extensive 
lateral roots. Marsdenia roots extend beyond 
750 mm deep and Pate & Dixon (1982) treat the 
species as deep-rooted, but further data are 
needed. 
ANATOMY 
Methods 
Seedling tissue 18 wk old was fixed in 5% glu- 
taraldehyde in phosphate buffer, dehydrated in 
a graded ethanol series and then infiltrated with 
LR White resin fBioRad’ Microscience Div¬ 
ision, Hemel Hempstead) over 72 hr and poly¬ 
merized at 65°C overnight. Thick sections were 
obtained using an American Optical Corp. 
Model 860 sledge microtome and stained with 
1% safranin (aqueous). 
Fig. 9. Rhyncharrhena linearis sucker shoots marked with flags at site 4. Mature plant from which the suckers are 
probably derived is approximately 10 m to the left of the photo inside the fenced plot. 
