The true lily and tulip family
Liliaceae was one of the largest families in botany and is now one of the more modest ones. That history is worth knowing rather than skipping, because it is the reason so many plants sold as lilies are not in this family at all and do not behave like the ones that are.
about 15 genera
roughly 700 species
The temperate northern hemisphere, centered on Asia, Europe and North America
For most of the twentieth century Liliaceae was where a monocot went when nobody was sure what else to do with it. Anything with six tepals, six stamens and a bulb tended to land here, and at its widest the family was reckoned to hold something like 250 genera and 4,000 species.
Comparing DNA rather than appearance took it apart. Plants had converged on a similar look without being closely related, so agaves, aloes, onions, asparagus, hostas and hyacinths were all moved out to families of their own. What is left is a much tighter group built around Lilium and Tulipa, with Fritillaria, Erythronium and the mariposa lilies alongside them.
This is not academic tidying. The plants that left really are different plants. They flower differently, they store food differently, and they differ in the one respect that matters most in a shop with a cat in it.
Open any member of this family and count. There are six segments in the perianth, in two rings of three, and in nearly all of them the outer three and the inner three look identical. When sepals and petals cannot be told apart, botany stops calling them either and calls them tepals. Six stamens follow, then a single ovary divided into three chambers.
The trouble is that the word lily was attached to plants long before anyone counted. Daylilies are Hemerocallis and sit in Asphodelaceae. Calla lilies and peace lilies are both aroids, and what looks like their flower is a spike wrapped in a modified leaf. Lily of the valley is in Asparagaceae, and water lilies are not close to any of them.
The test is the flower itself. A true lily opens six separate tepals from a bud that was pointed rather than rounded, and carries six anthers on long filaments that will stain whatever they touch.
True lilies are lethal to cats. Every part of a Lilium is toxic to them, including the pollen and the water in the vase, and the result is acute kidney failure that can follow a cat brushing past a stem and then washing its fur. Daylilies do the same thing, which is why a plant from another family belongs inside the same warning. There is no safe amount and no home remedy. It is a same day emergency for a veterinarian.
Calla lilies and peace lilies are a completely different problem and a much smaller one. Being aroids they carry calcium oxalate crystals, which burn the mouth and cause drooling and a refusal to eat. Unpleasant, and rarely dangerous.
Say it plainly to a customer with cats and offer them something else. Alstroemeria is sold as the Peruvian lily, is not a lily, and makes a reasonable substitute in both look and price.
A tulip stem is still alive in a way most cut flowers are not. It will lengthen in the vase, often by an inch or more across the first few days, and it bends toward light and away from gravity while it does. An arrangement that was even on Monday leans by Wednesday, and there is no correcting it, because the stem has genuinely grown into that shape.
Work with it instead. Cut tulips a little shorter than the finished height you want, keep them out of direct light and stand them cool. A bunch that has already flopped can be wrapped firmly in paper up to the heads and stood in deep water for an hour or two, which brings them back upright and holds them there for a while.
Lilies want the opposite sort of attention. Take the anthers off with a tissue as each bud opens, before the pollen has loosened. The stain does not come out of fabric, and removing them buys a few days as well, since a flower that cannot be pollinated stays open longer.
