noun, plural hy·dro·rhi·zae [hahy-druh-rahy-zee] /ˌhaɪ drəˈraɪ zi/.
Examples from the Web for hydrorhiza
The colonies are cylindrical tubes about one quarter of an inch in height, rising from a creeping stem (hydrorhiza).The Sea-beach at Ebb-tide|Augusta Foote Arnold
As a general rule polyp-buds are produced from the hydrorhiza and hydrocaulus, while medusa-buds are formed on the hydranth.
The foot by which it is attached often sends out root-like processes—the hydrorhiza (c).
In some cases, however, medusa-buds are formed on the hydrorhiza, as in Hydrocorallines.